// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/profiler/heap-snapshot-generator.h"

#include <utility>

#include "src/api-inl.h"
#include "src/assembler-inl.h"
#include "src/conversions.h"
#include "src/debug/debug.h"
#include "src/global-handles.h"
#include "src/layout-descriptor.h"
#include "src/objects-body-descriptors.h"
#include "src/objects-inl.h"
#include "src/objects/allocation-site-inl.h"
#include "src/objects/api-callbacks.h"
#include "src/objects/cell-inl.h"
#include "src/objects/feedback-cell-inl.h"
#include "src/objects/hash-table-inl.h"
#include "src/objects/js-array-buffer-inl.h"
#include "src/objects/js-array-inl.h"
#include "src/objects/js-collection-inl.h"
#include "src/objects/js-generator-inl.h"
#include "src/objects/js-promise-inl.h"
#include "src/objects/js-regexp-inl.h"
#include "src/objects/literal-objects-inl.h"
#include "src/objects/slots-inl.h"
#include "src/objects/struct-inl.h"
#include "src/profiler/allocation-tracker.h"
#include "src/profiler/heap-profiler.h"
#include "src/profiler/heap-snapshot-generator-inl.h"
#include "src/prototype.h"
#include "src/transitions-inl.h"
#include "src/vector.h"
#include "src/visitors.h"

namespace v8 {
namespace internal {

    HeapGraphEdge::HeapGraphEdge(Type type, const char* name, HeapEntry* from,
        HeapEntry* to)
        : bit_field_(TypeField::encode(type) | FromIndexField::encode(from->index()))
        , to_entry_(to)
        , name_(name)
    {
        DCHECK(type == kContextVariable
            || type == kProperty
            || type == kInternal
            || type == kShortcut
            || type == kWeak);
    }

    HeapGraphEdge::HeapGraphEdge(Type type, int index, HeapEntry* from,
        HeapEntry* to)
        : bit_field_(TypeField::encode(type) | FromIndexField::encode(from->index()))
        , to_entry_(to)
        , index_(index)
    {
        DCHECK(type == kElement || type == kHidden);
    }

    HeapEntry::HeapEntry(HeapSnapshot* snapshot, int index, Type type,
        const char* name, SnapshotObjectId id, size_t self_size,
        unsigned trace_node_id)
        : type_(type)
        , index_(index)
        , children_count_(0)
        , self_size_(self_size)
        , snapshot_(snapshot)
        , name_(name)
        , id_(id)
        , trace_node_id_(trace_node_id)
    {
        DCHECK_GE(index, 0);
    }

    void HeapEntry::SetNamedReference(HeapGraphEdge::Type type,
        const char* name,
        HeapEntry* entry)
    {
        ++children_count_;
        snapshot_->edges().emplace_back(type, name, this, entry);
    }

    void HeapEntry::SetIndexedReference(HeapGraphEdge::Type type,
        int index,
        HeapEntry* entry)
    {
        ++children_count_;
        snapshot_->edges().emplace_back(type, index, this, entry);
    }

    void HeapEntry::SetNamedAutoIndexReference(HeapGraphEdge::Type type,
        const char* description,
        HeapEntry* child,
        StringsStorage* names)
    {
        int index = children_count_ + 1;
        const char* name = description
            ? names->GetFormatted("%d / %s", index, description)
            : names->GetName(index);
        SetNamedReference(type, name, child);
    }

    void HeapEntry::Print(
        const char* prefix, const char* edge_name, int max_depth, int indent)
    {
        STATIC_ASSERT(sizeof(unsigned) == sizeof(id()));
        base::OS::Print("%6" PRIuS " @%6u %*c %s%s: ", self_size(), id(), indent, ' ',
            prefix, edge_name);
        if (type() != kString) {
            base::OS::Print("%s %.40s\n", TypeAsString(), name_);
        } else {
            base::OS::Print("\"");
            const char* c = name_;
            while (*c && (c - name_) <= 40) {
                if (*c != '\n')
                    base::OS::Print("%c", *c);
                else
                    base::OS::Print("\\n");
                ++c;
            }
            base::OS::Print("\"\n");
        }
        if (--max_depth == 0)
            return;
        for (auto i = children_begin(); i != children_end(); ++i) {
            HeapGraphEdge& edge = **i;
            const char* edge_prefix = "";
            EmbeddedVector<char, 64> index;
            const char* edge_name = index.start();
            switch (edge.type()) {
            case HeapGraphEdge::kContextVariable:
                edge_prefix = "#";
                edge_name = edge.name();
                break;
            case HeapGraphEdge::kElement:
                SNPrintF(index, "%d", edge.index());
                break;
            case HeapGraphEdge::kInternal:
                edge_prefix = "$";
                edge_name = edge.name();
                break;
            case HeapGraphEdge::kProperty:
                edge_name = edge.name();
                break;
            case HeapGraphEdge::kHidden:
                edge_prefix = "$";
                SNPrintF(index, "%d", edge.index());
                break;
            case HeapGraphEdge::kShortcut:
                edge_prefix = "^";
                edge_name = edge.name();
                break;
            case HeapGraphEdge::kWeak:
                edge_prefix = "w";
                edge_name = edge.name();
                break;
            default:
                SNPrintF(index, "!!! unknown edge type: %d ", edge.type());
            }
            edge.to()->Print(edge_prefix, edge_name, max_depth, indent + 2);
        }
    }

    const char* HeapEntry::TypeAsString()
    {
        switch (type()) {
        case kHidden:
            return "/hidden/";
        case kObject:
            return "/object/";
        case kClosure:
            return "/closure/";
        case kString:
            return "/string/";
        case kCode:
            return "/code/";
        case kArray:
            return "/array/";
        case kRegExp:
            return "/regexp/";
        case kHeapNumber:
            return "/number/";
        case kNative:
            return "/native/";
        case kSynthetic:
            return "/synthetic/";
        case kConsString:
            return "/concatenated string/";
        case kSlicedString:
            return "/sliced string/";
        case kSymbol:
            return "/symbol/";
        case kBigInt:
            return "/bigint/";
        default:
            return "???";
        }
    }

    HeapSnapshot::HeapSnapshot(HeapProfiler* profiler)
        : profiler_(profiler)
    {
        // It is very important to keep objects that form a heap snapshot
        // as small as possible. Check assumptions about data structure sizes.
        STATIC_ASSERT((kSystemPointerSize == 4 && sizeof(HeapGraphEdge) == 12) || (kSystemPointerSize == 8 && sizeof(HeapGraphEdge) == 24));
        STATIC_ASSERT((kSystemPointerSize == 4 && sizeof(HeapEntry) == 28) || (kSystemPointerSize == 8 && sizeof(HeapEntry) == 40));
        memset(&gc_subroot_entries_, 0, sizeof(gc_subroot_entries_));
    }

    void HeapSnapshot::Delete()
    {
        profiler_->RemoveSnapshot(this);
    }

    void HeapSnapshot::RememberLastJSObjectId()
    {
        max_snapshot_js_object_id_ = profiler_->heap_object_map()->last_assigned_id();
    }

    void HeapSnapshot::AddSyntheticRootEntries()
    {
        AddRootEntry();
        AddGcRootsEntry();
        SnapshotObjectId id = HeapObjectsMap::kGcRootsFirstSubrootId;
        for (int root = 0; root < static_cast<int>(Root::kNumberOfRoots); root++) {
            AddGcSubrootEntry(static_cast<Root>(root), id);
            id += HeapObjectsMap::kObjectIdStep;
        }
        DCHECK_EQ(HeapObjectsMap::kFirstAvailableObjectId, id);
    }

    void HeapSnapshot::AddRootEntry()
    {
        DCHECK_NULL(root_entry_);
        DCHECK(entries_.empty()); // Root entry must be the first one.
        root_entry_ = AddEntry(HeapEntry::kSynthetic, "",
            HeapObjectsMap::kInternalRootObjectId, 0, 0);
        DCHECK_EQ(1u, entries_.size());
        DCHECK_EQ(root_entry_, &entries_.front());
    }

    void HeapSnapshot::AddGcRootsEntry()
    {
        DCHECK_NULL(gc_roots_entry_);
        gc_roots_entry_ = AddEntry(HeapEntry::kSynthetic, "(GC roots)",
            HeapObjectsMap::kGcRootsObjectId, 0, 0);
    }

    void HeapSnapshot::AddGcSubrootEntry(Root root, SnapshotObjectId id)
    {
        DCHECK_NULL(gc_subroot_entries_[static_cast<int>(root)]);
        gc_subroot_entries_[static_cast<int>(root)] = AddEntry(HeapEntry::kSynthetic, RootVisitor::RootName(root), id, 0, 0);
    }

    void HeapSnapshot::AddLocation(HeapEntry* entry, int scriptId, int line,
        int col)
    {
        locations_.emplace_back(entry->index(), scriptId, line, col);
    }

    HeapEntry* HeapSnapshot::AddEntry(HeapEntry::Type type,
        const char* name,
        SnapshotObjectId id,
        size_t size,
        unsigned trace_node_id)
    {
        DCHECK(!is_complete());
        entries_.emplace_back(this, static_cast<int>(entries_.size()), type, name, id,
            size, trace_node_id);
        return &entries_.back();
    }

    void HeapSnapshot::FillChildren()
    {
        DCHECK(children().empty());
        int children_index = 0;
        for (HeapEntry& entry : entries()) {
            children_index = entry.set_children_index(children_index);
        }
        DCHECK_EQ(edges().size(), static_cast<size_t>(children_index));
        children().resize(edges().size());
        for (HeapGraphEdge& edge : edges()) {
            edge.from()->add_child(&edge);
        }
    }

    HeapEntry* HeapSnapshot::GetEntryById(SnapshotObjectId id)
    {
        if (entries_by_id_cache_.empty()) {
            CHECK(is_complete());
            entries_by_id_cache_.reserve(entries_.size());
            for (HeapEntry& entry : entries_) {
                entries_by_id_cache_.emplace(entry.id(), &entry);
            }
        }
        auto it = entries_by_id_cache_.find(id);
        return it != entries_by_id_cache_.end() ? it->second : nullptr;
    }

    void HeapSnapshot::Print(int max_depth)
    {
        root()->Print("", "", max_depth, 0);
    }

    // We split IDs on evens for embedder objects (see
    // HeapObjectsMap::GenerateId) and odds for native objects.
    const SnapshotObjectId HeapObjectsMap::kInternalRootObjectId = 1;
    const SnapshotObjectId HeapObjectsMap::kGcRootsObjectId = HeapObjectsMap::kInternalRootObjectId + HeapObjectsMap::kObjectIdStep;
    const SnapshotObjectId HeapObjectsMap::kGcRootsFirstSubrootId = HeapObjectsMap::kGcRootsObjectId + HeapObjectsMap::kObjectIdStep;
    const SnapshotObjectId HeapObjectsMap::kFirstAvailableObjectId = HeapObjectsMap::kGcRootsFirstSubrootId + static_cast<int>(Root::kNumberOfRoots) * HeapObjectsMap::kObjectIdStep;

    HeapObjectsMap::HeapObjectsMap(Heap* heap)
        : next_id_(kFirstAvailableObjectId)
        , heap_(heap)
    {
        // The dummy element at zero index is needed as entries_map_ cannot hold
        // an entry with zero value. Otherwise it's impossible to tell if
        // LookupOrInsert has added a new item or just returning exisiting one
        // having the value of zero.
        entries_.emplace_back(0, kNullAddress, 0, true);
    }

    bool HeapObjectsMap::MoveObject(Address from, Address to, int object_size)
    {
        DCHECK_NE(kNullAddress, to);
        DCHECK_NE(kNullAddress, from);
        if (from == to)
            return false;
        void* from_value = entries_map_.Remove(reinterpret_cast<void*>(from),
            ComputeAddressHash(from));
        if (from_value == nullptr) {
            // It may occur that some untracked object moves to an address X and there
            // is a tracked object at that address. In this case we should remove the
            // entry as we know that the object has died.
            void* to_value = entries_map_.Remove(reinterpret_cast<void*>(to),
                ComputeAddressHash(to));
            if (to_value != nullptr) {
                int to_entry_info_index = static_cast<int>(reinterpret_cast<intptr_t>(to_value));
                entries_.at(to_entry_info_index).addr = kNullAddress;
            }
        } else {
            base::HashMap::Entry* to_entry = entries_map_.LookupOrInsert(
                reinterpret_cast<void*>(to), ComputeAddressHash(to));
            if (to_entry->value != nullptr) {
                // We found the existing entry with to address for an old object.
                // Without this operation we will have two EntryInfo's with the same
                // value in addr field. It is bad because later at RemoveDeadEntries
                // one of this entry will be removed with the corresponding entries_map_
                // entry.
                int to_entry_info_index = static_cast<int>(reinterpret_cast<intptr_t>(to_entry->value));
                entries_.at(to_entry_info_index).addr = kNullAddress;
            }
            int from_entry_info_index = static_cast<int>(reinterpret_cast<intptr_t>(from_value));
            entries_.at(from_entry_info_index).addr = to;
            // Size of an object can change during its life, so to keep information
            // about the object in entries_ consistent, we have to adjust size when the
            // object is migrated.
            if (FLAG_heap_profiler_trace_objects) {
                PrintF("Move object from %p to %p old size %6d new size %6d\n",
                    reinterpret_cast<void*>(from), reinterpret_cast<void*>(to),
                    entries_.at(from_entry_info_index).size, object_size);
            }
            entries_.at(from_entry_info_index).size = object_size;
            to_entry->value = from_value;
        }
        return from_value != nullptr;
    }

    void HeapObjectsMap::UpdateObjectSize(Address addr, int size)
    {
        FindOrAddEntry(addr, size, false);
    }

    SnapshotObjectId HeapObjectsMap::FindEntry(Address addr)
    {
        base::HashMap::Entry* entry = entries_map_.Lookup(
            reinterpret_cast<void*>(addr), ComputeAddressHash(addr));
        if (entry == nullptr)
            return 0;
        int entry_index = static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
        EntryInfo& entry_info = entries_.at(entry_index);
        DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
        return entry_info.id;
    }

    SnapshotObjectId HeapObjectsMap::FindOrAddEntry(Address addr,
        unsigned int size,
        bool accessed)
    {
        DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
        base::HashMap::Entry* entry = entries_map_.LookupOrInsert(
            reinterpret_cast<void*>(addr), ComputeAddressHash(addr));
        if (entry->value != nullptr) {
            int entry_index = static_cast<int>(reinterpret_cast<intptr_t>(entry->value));
            EntryInfo& entry_info = entries_.at(entry_index);
            entry_info.accessed = accessed;
            if (FLAG_heap_profiler_trace_objects) {
                PrintF("Update object size : %p with old size %d and new size %d\n",
                    reinterpret_cast<void*>(addr), entry_info.size, size);
            }
            entry_info.size = size;
            return entry_info.id;
        }
        entry->value = reinterpret_cast<void*>(entries_.size());
        SnapshotObjectId id = next_id_;
        next_id_ += kObjectIdStep;
        entries_.push_back(EntryInfo(id, addr, size, accessed));
        DCHECK(static_cast<uint32_t>(entries_.size()) > entries_map_.occupancy());
        return id;
    }

    void HeapObjectsMap::StopHeapObjectsTracking() { time_intervals_.clear(); }

    void HeapObjectsMap::UpdateHeapObjectsMap()
    {
        if (FLAG_heap_profiler_trace_objects) {
            PrintF("Begin HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
                entries_map_.occupancy());
        }
        heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
            GarbageCollectionReason::kHeapProfiler);
        HeapIterator iterator(heap_);
        for (HeapObject obj = iterator.next(); !obj.is_null();
             obj = iterator.next()) {
            FindOrAddEntry(obj->address(), obj->Size());
            if (FLAG_heap_profiler_trace_objects) {
                PrintF("Update object      : %p %6d. Next address is %p\n",
                    reinterpret_cast<void*>(obj->address()), obj->Size(),
                    reinterpret_cast<void*>(obj->address() + obj->Size()));
            }
        }
        RemoveDeadEntries();
        if (FLAG_heap_profiler_trace_objects) {
            PrintF("End HeapObjectsMap::UpdateHeapObjectsMap. map has %d entries.\n",
                entries_map_.occupancy());
        }
    }

    SnapshotObjectId HeapObjectsMap::PushHeapObjectsStats(OutputStream* stream,
        int64_t* timestamp_us)
    {
        UpdateHeapObjectsMap();
        time_intervals_.emplace_back(next_id_);
        int prefered_chunk_size = stream->GetChunkSize();
        std::vector<v8::HeapStatsUpdate> stats_buffer;
        DCHECK(!entries_.empty());
        EntryInfo* entry_info = &entries_.front();
        EntryInfo* end_entry_info = &entries_.back() + 1;
        for (size_t time_interval_index = 0;
             time_interval_index < time_intervals_.size(); ++time_interval_index) {
            TimeInterval& time_interval = time_intervals_[time_interval_index];
            SnapshotObjectId time_interval_id = time_interval.id;
            uint32_t entries_size = 0;
            EntryInfo* start_entry_info = entry_info;
            while (entry_info < end_entry_info && entry_info->id < time_interval_id) {
                entries_size += entry_info->size;
                ++entry_info;
            }
            uint32_t entries_count = static_cast<uint32_t>(entry_info - start_entry_info);
            if (time_interval.count != entries_count || time_interval.size != entries_size) {
                stats_buffer.emplace_back(static_cast<uint32_t>(time_interval_index),
                    time_interval.count = entries_count,
                    time_interval.size = entries_size);
                if (static_cast<int>(stats_buffer.size()) >= prefered_chunk_size) {
                    OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
                        &stats_buffer.front(), static_cast<int>(stats_buffer.size()));
                    if (result == OutputStream::kAbort)
                        return last_assigned_id();
                    stats_buffer.clear();
                }
            }
        }
        DCHECK(entry_info == end_entry_info);
        if (!stats_buffer.empty()) {
            OutputStream::WriteResult result = stream->WriteHeapStatsChunk(
                &stats_buffer.front(), static_cast<int>(stats_buffer.size()));
            if (result == OutputStream::kAbort)
                return last_assigned_id();
        }
        stream->EndOfStream();
        if (timestamp_us) {
            *timestamp_us = (time_intervals_.back().timestamp - time_intervals_.front().timestamp)
                                .InMicroseconds();
        }
        return last_assigned_id();
    }

    void HeapObjectsMap::RemoveDeadEntries()
    {
        DCHECK(entries_.size() > 0 && entries_.at(0).id == 0 && entries_.at(0).addr == kNullAddress);
        size_t first_free_entry = 1;
        for (size_t i = 1; i < entries_.size(); ++i) {
            EntryInfo& entry_info = entries_.at(i);
            if (entry_info.accessed) {
                if (first_free_entry != i) {
                    entries_.at(first_free_entry) = entry_info;
                }
                entries_.at(first_free_entry).accessed = false;
                base::HashMap::Entry* entry = entries_map_.Lookup(reinterpret_cast<void*>(entry_info.addr),
                    ComputeAddressHash(entry_info.addr));
                DCHECK(entry);
                entry->value = reinterpret_cast<void*>(first_free_entry);
                ++first_free_entry;
            } else {
                if (entry_info.addr) {
                    entries_map_.Remove(reinterpret_cast<void*>(entry_info.addr),
                        ComputeAddressHash(entry_info.addr));
                }
            }
        }
        entries_.erase(entries_.begin() + first_free_entry, entries_.end());

        DCHECK(static_cast<uint32_t>(entries_.size()) - 1 == entries_map_.occupancy());
    }

    V8HeapExplorer::V8HeapExplorer(HeapSnapshot* snapshot,
        SnapshottingProgressReportingInterface* progress,
        v8::HeapProfiler::ObjectNameResolver* resolver)
        : heap_(snapshot->profiler()->heap_object_map()->heap())
        , snapshot_(snapshot)
        , names_(snapshot_->profiler()->names())
        , heap_object_map_(snapshot_->profiler()->heap_object_map())
        , progress_(progress)
        , generator_(nullptr)
        , global_object_name_resolver_(resolver)
    {
    }

    HeapEntry* V8HeapExplorer::AllocateEntry(HeapThing ptr)
    {
        return AddEntry(HeapObject::cast(Object(reinterpret_cast<Address>(ptr))));
    }

    void V8HeapExplorer::ExtractLocation(HeapEntry* entry, HeapObject object)
    {
        if (object->IsJSFunction()) {
            JSFunction func = JSFunction::cast(object);
            ExtractLocationForJSFunction(entry, func);

        } else if (object->IsJSGeneratorObject()) {
            JSGeneratorObject gen = JSGeneratorObject::cast(object);
            ExtractLocationForJSFunction(entry, gen->function());

        } else if (object->IsJSObject()) {
            JSObject obj = JSObject::cast(object);
            JSFunction maybe_constructor = GetConstructor(obj);

            if (!maybe_constructor.is_null()) {
                ExtractLocationForJSFunction(entry, maybe_constructor);
            }
        }
    }

    void V8HeapExplorer::ExtractLocationForJSFunction(HeapEntry* entry,
        JSFunction func)
    {
        if (!func->shared()->script()->IsScript())
            return;
        Script script = Script::cast(func->shared()->script());
        int scriptId = script->id();
        int start = func->shared()->StartPosition();
        int line = script->GetLineNumber(start);
        int col = script->GetColumnNumber(start);
        snapshot_->AddLocation(entry, scriptId, line, col);
    }

    HeapEntry* V8HeapExplorer::AddEntry(HeapObject object)
    {
        if (object->IsJSFunction()) {
            JSFunction func = JSFunction::cast(object);
            SharedFunctionInfo shared = func->shared();
            const char* name = names_->GetName(shared->Name());
            return AddEntry(object, HeapEntry::kClosure, name);
        } else if (object->IsJSBoundFunction()) {
            return AddEntry(object, HeapEntry::kClosure, "native_bind");
        } else if (object->IsJSRegExp()) {
            JSRegExp re = JSRegExp::cast(object);
            return AddEntry(object,
                HeapEntry::kRegExp,
                names_->GetName(re->Pattern()));
        } else if (object->IsJSObject()) {
            const char* name = names_->GetName(
                GetConstructorName(JSObject::cast(object)));
            if (object->IsJSGlobalObject()) {
                auto it = objects_tags_.find(JSGlobalObject::cast(object));
                if (it != objects_tags_.end()) {
                    name = names_->GetFormatted("%s / %s", name, it->second);
                }
            }
            return AddEntry(object, HeapEntry::kObject, name);
        } else if (object->IsString()) {
            String string = String::cast(object);
            if (string->IsConsString()) {
                return AddEntry(object, HeapEntry::kConsString, "(concatenated string)");
            } else if (string->IsSlicedString()) {
                return AddEntry(object, HeapEntry::kSlicedString, "(sliced string)");
            } else {
                return AddEntry(object, HeapEntry::kString,
                    names_->GetName(String::cast(object)));
            }
        } else if (object->IsSymbol()) {
            if (Symbol::cast(object)->is_private())
                return AddEntry(object, HeapEntry::kHidden, "private symbol");
            else
                return AddEntry(object, HeapEntry::kSymbol, "symbol");
        } else if (object->IsBigInt()) {
            return AddEntry(object, HeapEntry::kBigInt, "bigint");
        } else if (object->IsCode()) {
            return AddEntry(object, HeapEntry::kCode, "");
        } else if (object->IsSharedFunctionInfo()) {
            String name = SharedFunctionInfo::cast(object)->Name();
            return AddEntry(object, HeapEntry::kCode, names_->GetName(name));
        } else if (object->IsScript()) {
            Object name = Script::cast(object)->name();
            return AddEntry(
                object, HeapEntry::kCode,
                name->IsString() ? names_->GetName(String::cast(name)) : "");
        } else if (object->IsNativeContext()) {
            return AddEntry(object, HeapEntry::kHidden, "system / NativeContext");
        } else if (object->IsContext()) {
            return AddEntry(object, HeapEntry::kObject, "system / Context");
        } else if (object->IsFixedArray() || object->IsFixedDoubleArray() || object->IsByteArray()) {
            return AddEntry(object, HeapEntry::kArray, "");
        } else if (object->IsHeapNumber()) {
            return AddEntry(object, HeapEntry::kHeapNumber, "number");
        }
        return AddEntry(object, HeapEntry::kHidden, GetSystemEntryName(object));
    }

    HeapEntry* V8HeapExplorer::AddEntry(HeapObject object, HeapEntry::Type type,
        const char* name)
    {
        return AddEntry(object->address(), type, name, object->Size());
    }

    HeapEntry* V8HeapExplorer::AddEntry(Address address,
        HeapEntry::Type type,
        const char* name,
        size_t size)
    {
        SnapshotObjectId object_id = heap_object_map_->FindOrAddEntry(
            address, static_cast<unsigned int>(size));
        unsigned trace_node_id = 0;
        if (AllocationTracker* allocation_tracker = snapshot_->profiler()->allocation_tracker()) {
            trace_node_id = allocation_tracker->address_to_trace()->GetTraceNodeId(address);
        }
        return snapshot_->AddEntry(type, name, object_id, size, trace_node_id);
    }

    const char* V8HeapExplorer::GetSystemEntryName(HeapObject object)
    {
        switch (object->map()->instance_type()) {
        case MAP_TYPE:
            switch (Map::cast(object)->instance_type()) {
#define MAKE_STRING_MAP_CASE(instance_type, size, name, Name) \
    case instance_type:                                       \
        return "system / Map (" #Name ")";
                STRING_TYPE_LIST(MAKE_STRING_MAP_CASE)
#undef MAKE_STRING_MAP_CASE
            default:
                return "system / Map";
            }
        case CELL_TYPE:
            return "system / Cell";
        case PROPERTY_CELL_TYPE:
            return "system / PropertyCell";
        case FOREIGN_TYPE:
            return "system / Foreign";
        case ODDBALL_TYPE:
            return "system / Oddball";
        case ALLOCATION_SITE_TYPE:
            return "system / AllocationSite";
#define MAKE_STRUCT_CASE(TYPE, Name, name) \
    case TYPE:                             \
        return "system / " #Name;
            STRUCT_LIST(MAKE_STRUCT_CASE)
#undef MAKE_STRUCT_CASE
        default:
            return "system";
        }
    }

    int V8HeapExplorer::EstimateObjectsCount()
    {
        HeapIterator it(heap_, HeapIterator::kFilterUnreachable);
        int objects_count = 0;
        while (!it.next().is_null())
            ++objects_count;
        return objects_count;
    }

    class IndexedReferencesExtractor : public ObjectVisitor {
    public:
        IndexedReferencesExtractor(V8HeapExplorer* generator, HeapObject parent_obj,
            HeapEntry* parent)
            : generator_(generator)
            , parent_obj_(parent_obj)
            , parent_start_(parent_obj_.RawMaybeWeakField(0))
            , parent_end_(parent_obj_.RawMaybeWeakField(parent_obj_->Size()))
            , parent_(parent)
            , next_index_(0)
        {
        }
        void VisitPointers(HeapObject host, ObjectSlot start,
            ObjectSlot end) override
        {
            VisitPointers(host, MaybeObjectSlot(start), MaybeObjectSlot(end));
        }
        void VisitPointers(HeapObject host, MaybeObjectSlot start,
            MaybeObjectSlot end) override
        {
            // [start,end) must be a sub-region of [parent_start_, parent_end), i.e.
            // all the slots must point inside the object.
            CHECK_LE(parent_start_, start);
            CHECK_LE(end, parent_end_);
            for (MaybeObjectSlot p = start; p < end; ++p) {
                int field_index = static_cast<int>(p - parent_start_);
                if (generator_->visited_fields_[field_index]) {
                    generator_->visited_fields_[field_index] = false;
                    continue;
                }
                HeapObject heap_object;
                if ((*p)->GetHeapObject(&heap_object)) {
                    VisitHeapObjectImpl(heap_object, field_index);
                }
            }
        }

        void VisitCodeTarget(Code host, RelocInfo* rinfo) override
        {
            Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
            VisitHeapObjectImpl(target, -1);
        }

        void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override
        {
            VisitHeapObjectImpl(rinfo->target_object(), -1);
        }

    private:
        V8_INLINE void VisitHeapObjectImpl(HeapObject heap_object, int field_index)
        {
            DCHECK_LE(-1, field_index);
            // The last parameter {field_offset} is only used to check some well-known
            // skipped references, so passing -1 * kTaggedSize for objects embedded
            // into code is fine.
            generator_->SetHiddenReference(parent_obj_, parent_, next_index_++,
                heap_object, field_index * kTaggedSize);
        }

        V8HeapExplorer* generator_;
        HeapObject parent_obj_;
        MaybeObjectSlot parent_start_;
        MaybeObjectSlot parent_end_;
        HeapEntry* parent_;
        int next_index_;
    };

    void V8HeapExplorer::ExtractReferences(HeapEntry* entry, HeapObject obj)
    {
        if (obj->IsJSGlobalProxy()) {
            ExtractJSGlobalProxyReferences(entry, JSGlobalProxy::cast(obj));
        } else if (obj->IsJSArrayBuffer()) {
            ExtractJSArrayBufferReferences(entry, JSArrayBuffer::cast(obj));
        } else if (obj->IsJSObject()) {
            if (obj->IsJSWeakSet()) {
                ExtractJSWeakCollectionReferences(entry, JSWeakSet::cast(obj));
            } else if (obj->IsJSWeakMap()) {
                ExtractJSWeakCollectionReferences(entry, JSWeakMap::cast(obj));
            } else if (obj->IsJSSet()) {
                ExtractJSCollectionReferences(entry, JSSet::cast(obj));
            } else if (obj->IsJSMap()) {
                ExtractJSCollectionReferences(entry, JSMap::cast(obj));
            } else if (obj->IsJSPromise()) {
                ExtractJSPromiseReferences(entry, JSPromise::cast(obj));
            } else if (obj->IsJSGeneratorObject()) {
                ExtractJSGeneratorObjectReferences(entry, JSGeneratorObject::cast(obj));
            }
            ExtractJSObjectReferences(entry, JSObject::cast(obj));
        } else if (obj->IsString()) {
            ExtractStringReferences(entry, String::cast(obj));
        } else if (obj->IsSymbol()) {
            ExtractSymbolReferences(entry, Symbol::cast(obj));
        } else if (obj->IsMap()) {
            ExtractMapReferences(entry, Map::cast(obj));
        } else if (obj->IsSharedFunctionInfo()) {
            ExtractSharedFunctionInfoReferences(entry, SharedFunctionInfo::cast(obj));
        } else if (obj->IsScript()) {
            ExtractScriptReferences(entry, Script::cast(obj));
        } else if (obj->IsAccessorInfo()) {
            ExtractAccessorInfoReferences(entry, AccessorInfo::cast(obj));
        } else if (obj->IsAccessorPair()) {
            ExtractAccessorPairReferences(entry, AccessorPair::cast(obj));
        } else if (obj->IsCode()) {
            ExtractCodeReferences(entry, Code::cast(obj));
        } else if (obj->IsCell()) {
            ExtractCellReferences(entry, Cell::cast(obj));
        } else if (obj->IsFeedbackCell()) {
            ExtractFeedbackCellReferences(entry, FeedbackCell::cast(obj));
        } else if (obj->IsPropertyCell()) {
            ExtractPropertyCellReferences(entry, PropertyCell::cast(obj));
        } else if (obj->IsAllocationSite()) {
            ExtractAllocationSiteReferences(entry, AllocationSite::cast(obj));
        } else if (obj->IsArrayBoilerplateDescription()) {
            ExtractArrayBoilerplateDescriptionReferences(
                entry, ArrayBoilerplateDescription::cast(obj));
        } else if (obj->IsFeedbackVector()) {
            ExtractFeedbackVectorReferences(entry, FeedbackVector::cast(obj));
        } else if (obj->IsDescriptorArray()) {
            ExtractDescriptorArrayReferences(entry, DescriptorArray::cast(obj));
        } else if (obj->IsWeakFixedArray()) {
            ExtractWeakArrayReferences(WeakFixedArray::kHeaderSize, entry,
                WeakFixedArray::cast(obj));
        } else if (obj->IsWeakArrayList()) {
            ExtractWeakArrayReferences(WeakArrayList::kHeaderSize, entry,
                WeakArrayList::cast(obj));
        } else if (obj->IsContext()) {
            ExtractContextReferences(entry, Context::cast(obj));
        } else if (obj->IsEphemeronHashTable()) {
            ExtractEphemeronHashTableReferences(entry, EphemeronHashTable::cast(obj));
        } else if (obj->IsFixedArray()) {
            ExtractFixedArrayReferences(entry, FixedArray::cast(obj));
        }
    }

    void V8HeapExplorer::ExtractJSGlobalProxyReferences(HeapEntry* entry,
        JSGlobalProxy proxy)
    {
        SetInternalReference(entry, "native_context", proxy->native_context(),
            JSGlobalProxy::kNativeContextOffset);
    }

    void V8HeapExplorer::ExtractJSObjectReferences(HeapEntry* entry,
        JSObject js_obj)
    {
        HeapObject obj = js_obj;
        ExtractPropertyReferences(js_obj, entry);
        ExtractElementReferences(js_obj, entry);
        ExtractInternalReferences(js_obj, entry);
        Isolate* isolate = Isolate::FromHeap(heap_);
        PrototypeIterator iter(isolate, js_obj);
        ReadOnlyRoots roots(isolate);
        SetPropertyReference(entry, roots.proto_string(), iter.GetCurrent());
        if (obj->IsJSBoundFunction()) {
            JSBoundFunction js_fun = JSBoundFunction::cast(obj);
            TagObject(js_fun->bound_arguments(), "(bound arguments)");
            SetInternalReference(entry, "bindings", js_fun->bound_arguments(),
                JSBoundFunction::kBoundArgumentsOffset);
            SetInternalReference(entry, "bound_this", js_fun->bound_this(),
                JSBoundFunction::kBoundThisOffset);
            SetInternalReference(entry, "bound_function",
                js_fun->bound_target_function(),
                JSBoundFunction::kBoundTargetFunctionOffset);
            FixedArray bindings = js_fun->bound_arguments();
            for (int i = 0; i < bindings->length(); i++) {
                const char* reference_name = names_->GetFormatted("bound_argument_%d", i);
                SetNativeBindReference(entry, reference_name, bindings->get(i));
            }
        } else if (obj->IsJSFunction()) {
            JSFunction js_fun = JSFunction::cast(js_obj);
            if (js_fun->has_prototype_slot()) {
                Object proto_or_map = js_fun->prototype_or_initial_map();
                if (!proto_or_map->IsTheHole(isolate)) {
                    if (!proto_or_map->IsMap()) {
                        SetPropertyReference(entry, roots.prototype_string(), proto_or_map,
                            nullptr,
                            JSFunction::kPrototypeOrInitialMapOffset);
                    } else {
                        SetPropertyReference(entry, roots.prototype_string(),
                            js_fun->prototype());
                        SetInternalReference(entry, "initial_map", proto_or_map,
                            JSFunction::kPrototypeOrInitialMapOffset);
                    }
                }
            }
            SharedFunctionInfo shared_info = js_fun->shared();
            TagObject(js_fun->raw_feedback_cell(), "(function feedback cell)");
            SetInternalReference(entry, "feedback_cell", js_fun->raw_feedback_cell(),
                JSFunction::kFeedbackCellOffset);
            TagObject(shared_info, "(shared function info)");
            SetInternalReference(entry, "shared", shared_info,
                JSFunction::kSharedFunctionInfoOffset);
            TagObject(js_fun->context(), "(context)");
            SetInternalReference(entry, "context", js_fun->context(),
                JSFunction::kContextOffset);
            SetInternalReference(entry, "code", js_fun->code(),
                JSFunction::kCodeOffset);
        } else if (obj->IsJSGlobalObject()) {
            JSGlobalObject global_obj = JSGlobalObject::cast(obj);
            SetInternalReference(entry, "native_context", global_obj->native_context(),
                JSGlobalObject::kNativeContextOffset);
            SetInternalReference(entry, "global_proxy", global_obj->global_proxy(),
                JSGlobalObject::kGlobalProxyOffset);
            STATIC_ASSERT(JSGlobalObject::kSize - JSObject::kHeaderSize == 2 * kTaggedSize);
        } else if (obj->IsJSArrayBufferView()) {
            JSArrayBufferView view = JSArrayBufferView::cast(obj);
            SetInternalReference(entry, "buffer", view->buffer(),
                JSArrayBufferView::kBufferOffset);
        }

        TagObject(js_obj->raw_properties_or_hash(), "(object properties)");
        SetInternalReference(entry, "properties", js_obj->raw_properties_or_hash(),
            JSObject::kPropertiesOrHashOffset);

        TagObject(js_obj->elements(), "(object elements)");
        SetInternalReference(entry, "elements", js_obj->elements(),
            JSObject::kElementsOffset);
    }

    void V8HeapExplorer::ExtractStringReferences(HeapEntry* entry, String string)
    {
        if (string->IsConsString()) {
            ConsString cs = ConsString::cast(string);
            SetInternalReference(entry, "first", cs->first(), ConsString::kFirstOffset);
            SetInternalReference(entry, "second", cs->second(),
                ConsString::kSecondOffset);
        } else if (string->IsSlicedString()) {
            SlicedString ss = SlicedString::cast(string);
            SetInternalReference(entry, "parent", ss->parent(),
                SlicedString::kParentOffset);
        } else if (string->IsThinString()) {
            ThinString ts = ThinString::cast(string);
            SetInternalReference(entry, "actual", ts->actual(),
                ThinString::kActualOffset);
        }
    }

    void V8HeapExplorer::ExtractSymbolReferences(HeapEntry* entry, Symbol symbol)
    {
        SetInternalReference(entry, "name", symbol->name(), Symbol::kNameOffset);
    }

    void V8HeapExplorer::ExtractJSCollectionReferences(HeapEntry* entry,
        JSCollection collection)
    {
        SetInternalReference(entry, "table", collection->table(),
            JSCollection::kTableOffset);
    }

    void V8HeapExplorer::ExtractJSWeakCollectionReferences(HeapEntry* entry,
        JSWeakCollection obj)
    {
        SetInternalReference(entry, "table", obj->table(),
            JSWeakCollection::kTableOffset);
    }

    void V8HeapExplorer::ExtractEphemeronHashTableReferences(
        HeapEntry* entry, EphemeronHashTable table)
    {
        for (int i = 0, capacity = table->Capacity(); i < capacity; ++i) {
            int key_index = EphemeronHashTable::EntryToIndex(i) + EphemeronHashTable::kEntryKeyIndex;
            int value_index = EphemeronHashTable::EntryToValueIndex(i);
            Object key = table->get(key_index);
            Object value = table->get(value_index);
            SetWeakReference(entry, key_index, key,
                table->OffsetOfElementAt(key_index));
            SetWeakReference(entry, value_index, value,
                table->OffsetOfElementAt(value_index));
            HeapEntry* key_entry = GetEntry(key);
            HeapEntry* value_entry = GetEntry(value);
            if (key_entry && value_entry) {
                const char* edge_name = names_->GetFormatted("key %s in WeakMap", key_entry->name());
                key_entry->SetNamedAutoIndexReference(HeapGraphEdge::kInternal, edge_name,
                    value_entry, names_);
            }
        }
    }

    // These static arrays are used to prevent excessive code-size in
    // ExtractContextReferences below, which would happen if we called
    // SetInternalReference for every native context field in a macro.
    static const struct {
        int index;
        const char* name;
    } native_context_names[] = {
#define CONTEXT_FIELD_INDEX_NAME(index, _, name) { Context::index, #name },
        NATIVE_CONTEXT_FIELDS(CONTEXT_FIELD_INDEX_NAME)
#undef CONTEXT_FIELD_INDEX_NAME
    };

    void V8HeapExplorer::ExtractContextReferences(HeapEntry* entry,
        Context context)
    {
        if (!context->IsNativeContext() && context->is_declaration_context()) {
            ScopeInfo scope_info = context->scope_info();
            // Add context allocated locals.
            int context_locals = scope_info->ContextLocalCount();
            for (int i = 0; i < context_locals; ++i) {
                String local_name = scope_info->ContextLocalName(i);
                int idx = Context::MIN_CONTEXT_SLOTS + i;
                SetContextReference(entry, local_name, context->get(idx),
                    Context::OffsetOfElementAt(idx));
            }
            if (scope_info->HasFunctionName()) {
                String name = String::cast(scope_info->FunctionName());
                int idx = scope_info->FunctionContextSlotIndex(name);
                if (idx >= 0) {
                    SetContextReference(entry, name, context->get(idx),
                        Context::OffsetOfElementAt(idx));
                }
            }
        }

        SetInternalReference(
            entry, "scope_info", context->get(Context::SCOPE_INFO_INDEX),
            FixedArray::OffsetOfElementAt(Context::SCOPE_INFO_INDEX));
        SetInternalReference(entry, "previous", context->get(Context::PREVIOUS_INDEX),
            FixedArray::OffsetOfElementAt(Context::PREVIOUS_INDEX));
        SetInternalReference(entry, "extension",
            context->get(Context::EXTENSION_INDEX),
            FixedArray::OffsetOfElementAt(Context::EXTENSION_INDEX));
        SetInternalReference(
            entry, "native_context", context->get(Context::NATIVE_CONTEXT_INDEX),
            FixedArray::OffsetOfElementAt(Context::NATIVE_CONTEXT_INDEX));

        if (context->IsNativeContext()) {
            TagObject(context->normalized_map_cache(), "(context norm. map cache)");
            TagObject(context->embedder_data(), "(context data)");
            for (size_t i = 0; i < arraysize(native_context_names); i++) {
                int index = native_context_names[i].index;
                const char* name = native_context_names[i].name;
                SetInternalReference(entry, name, context->get(index),
                    FixedArray::OffsetOfElementAt(index));
            }

            SetWeakReference(
                entry, "optimized_code_list",
                context->get(Context::OPTIMIZED_CODE_LIST),
                FixedArray::OffsetOfElementAt(Context::OPTIMIZED_CODE_LIST));
            SetWeakReference(
                entry, "deoptimized_code_list",
                context->get(Context::DEOPTIMIZED_CODE_LIST),
                FixedArray::OffsetOfElementAt(Context::DEOPTIMIZED_CODE_LIST));
            STATIC_ASSERT(Context::OPTIMIZED_CODE_LIST == Context::FIRST_WEAK_SLOT);
            STATIC_ASSERT(Context::NEXT_CONTEXT_LINK + 1 == Context::NATIVE_CONTEXT_SLOTS);
            STATIC_ASSERT(Context::FIRST_WEAK_SLOT + 3 == Context::NATIVE_CONTEXT_SLOTS);
        }
    }

    void V8HeapExplorer::ExtractMapReferences(HeapEntry* entry, Map map)
    {
        MaybeObject maybe_raw_transitions_or_prototype_info = map->raw_transitions();
        HeapObject raw_transitions_or_prototype_info;
        if (maybe_raw_transitions_or_prototype_info->GetHeapObjectIfWeak(
                &raw_transitions_or_prototype_info)) {
            DCHECK(raw_transitions_or_prototype_info->IsMap());
            SetWeakReference(entry, "transition", raw_transitions_or_prototype_info,
                Map::kTransitionsOrPrototypeInfoOffset);
        } else if (maybe_raw_transitions_or_prototype_info->GetHeapObjectIfStrong(
                       &raw_transitions_or_prototype_info)) {
            if (raw_transitions_or_prototype_info->IsTransitionArray()) {
                TransitionArray transitions = TransitionArray::cast(raw_transitions_or_prototype_info);
                if (map->CanTransition() && transitions->HasPrototypeTransitions()) {
                    TagObject(transitions->GetPrototypeTransitions(),
                        "(prototype transitions)");
                }
                TagObject(transitions, "(transition array)");
                SetInternalReference(entry, "transitions", transitions,
                    Map::kTransitionsOrPrototypeInfoOffset);
            } else if (raw_transitions_or_prototype_info->IsTuple3() || raw_transitions_or_prototype_info->IsFixedArray()) {
                TagObject(raw_transitions_or_prototype_info, "(transition)");
                SetInternalReference(entry, "transition",
                    raw_transitions_or_prototype_info,
                    Map::kTransitionsOrPrototypeInfoOffset);
            } else if (map->is_prototype_map()) {
                TagObject(raw_transitions_or_prototype_info, "prototype_info");
                SetInternalReference(entry, "prototype_info",
                    raw_transitions_or_prototype_info,
                    Map::kTransitionsOrPrototypeInfoOffset);
            }
        }
        DescriptorArray descriptors = map->instance_descriptors();
        TagObject(descriptors, "(map descriptors)");
        SetInternalReference(entry, "descriptors", descriptors,
            Map::kDescriptorsOffset);
        SetInternalReference(entry, "prototype", map->prototype(),
            Map::kPrototypeOffset);
        if (FLAG_unbox_double_fields) {
            SetInternalReference(entry, "layout_descriptor", map->layout_descriptor(),
                Map::kLayoutDescriptorOffset);
        }
        Object constructor_or_backpointer = map->constructor_or_backpointer();
        if (constructor_or_backpointer->IsMap()) {
            TagObject(constructor_or_backpointer, "(back pointer)");
            SetInternalReference(entry, "back_pointer", constructor_or_backpointer,
                Map::kConstructorOrBackPointerOffset);
        } else if (constructor_or_backpointer->IsFunctionTemplateInfo()) {
            TagObject(constructor_or_backpointer, "(constructor function data)");
            SetInternalReference(entry, "constructor_function_data",
                constructor_or_backpointer,
                Map::kConstructorOrBackPointerOffset);
        } else {
            SetInternalReference(entry, "constructor", constructor_or_backpointer,
                Map::kConstructorOrBackPointerOffset);
        }
        TagObject(map->dependent_code(), "(dependent code)");
        SetInternalReference(entry, "dependent_code", map->dependent_code(),
            Map::kDependentCodeOffset);
    }

    void V8HeapExplorer::ExtractSharedFunctionInfoReferences(
        HeapEntry* entry, SharedFunctionInfo shared)
    {
        String shared_name = shared->DebugName();
        const char* name = nullptr;
        if (shared_name != ReadOnlyRoots(heap_).empty_string()) {
            name = names_->GetName(shared_name);
            TagObject(shared->GetCode(), names_->GetFormatted("(code for %s)", name));
        } else {
            TagObject(shared->GetCode(),
                names_->GetFormatted(
                    "(%s code)", Code::Kind2String(shared->GetCode()->kind())));
        }

        if (shared->name_or_scope_info()->IsScopeInfo()) {
            TagObject(shared->name_or_scope_info(), "(function scope info)");
        }
        SetInternalReference(entry, "name_or_scope_info",
            shared->name_or_scope_info(),
            SharedFunctionInfo::kNameOrScopeInfoOffset);
        SetInternalReference(entry, "script_or_debug_info",
            shared->script_or_debug_info(),
            SharedFunctionInfo::kScriptOrDebugInfoOffset);
        SetInternalReference(entry, "function_data", shared->function_data(),
            SharedFunctionInfo::kFunctionDataOffset);
        SetInternalReference(
            entry, "raw_outer_scope_info_or_feedback_metadata",
            shared->raw_outer_scope_info_or_feedback_metadata(),
            SharedFunctionInfo::kOuterScopeInfoOrFeedbackMetadataOffset);
    }

    void V8HeapExplorer::ExtractScriptReferences(HeapEntry* entry, Script script)
    {
        SetInternalReference(entry, "source", script->source(),
            Script::kSourceOffset);
        SetInternalReference(entry, "name", script->name(), Script::kNameOffset);
        SetInternalReference(entry, "context_data", script->context_data(),
            Script::kContextOffset);
        TagObject(script->line_ends(), "(script line ends)");
        SetInternalReference(entry, "line_ends", script->line_ends(),
            Script::kLineEndsOffset);
    }

    void V8HeapExplorer::ExtractAccessorInfoReferences(HeapEntry* entry,
        AccessorInfo accessor_info)
    {
        SetInternalReference(entry, "name", accessor_info->name(),
            AccessorInfo::kNameOffset);
        SetInternalReference(entry, "expected_receiver_type",
            accessor_info->expected_receiver_type(),
            AccessorInfo::kExpectedReceiverTypeOffset);
        SetInternalReference(entry, "getter", accessor_info->getter(),
            AccessorInfo::kGetterOffset);
        SetInternalReference(entry, "setter", accessor_info->setter(),
            AccessorInfo::kSetterOffset);
        SetInternalReference(entry, "data", accessor_info->data(),
            AccessorInfo::kDataOffset);
    }

    void V8HeapExplorer::ExtractAccessorPairReferences(HeapEntry* entry,
        AccessorPair accessors)
    {
        SetInternalReference(entry, "getter", accessors->getter(),
            AccessorPair::kGetterOffset);
        SetInternalReference(entry, "setter", accessors->setter(),
            AccessorPair::kSetterOffset);
    }

    void V8HeapExplorer::TagBuiltinCodeObject(Code code, const char* name)
    {
        TagObject(code, names_->GetFormatted("(%s builtin)", name));
    }

    void V8HeapExplorer::ExtractCodeReferences(HeapEntry* entry, Code code)
    {
        TagObject(code->relocation_info(), "(code relocation info)");
        SetInternalReference(entry, "relocation_info", code->relocation_info(),
            Code::kRelocationInfoOffset);
        TagObject(code->deoptimization_data(), "(code deopt data)");
        SetInternalReference(entry, "deoptimization_data",
            code->deoptimization_data(),
            Code::kDeoptimizationDataOffset);
        TagObject(code->source_position_table(), "(source position table)");
        SetInternalReference(entry, "source_position_table",
            code->source_position_table(),
            Code::kSourcePositionTableOffset);
    }

    void V8HeapExplorer::ExtractCellReferences(HeapEntry* entry, Cell cell)
    {
        SetInternalReference(entry, "value", cell->value(), Cell::kValueOffset);
    }

    void V8HeapExplorer::ExtractFeedbackCellReferences(HeapEntry* entry,
        FeedbackCell feedback_cell)
    {
        TagObject(feedback_cell, "(feedback cell)");
        SetInternalReference(entry, "value", feedback_cell->value(),
            FeedbackCell::kValueOffset);
    }

    void V8HeapExplorer::ExtractPropertyCellReferences(HeapEntry* entry,
        PropertyCell cell)
    {
        SetInternalReference(entry, "value", cell->value(),
            PropertyCell::kValueOffset);
        TagObject(cell->dependent_code(), "(dependent code)");
        SetInternalReference(entry, "dependent_code", cell->dependent_code(),
            PropertyCell::kDependentCodeOffset);
    }

    void V8HeapExplorer::ExtractAllocationSiteReferences(HeapEntry* entry,
        AllocationSite site)
    {
        SetInternalReference(entry, "transition_info",
            site->transition_info_or_boilerplate(),
            AllocationSite::kTransitionInfoOrBoilerplateOffset);
        SetInternalReference(entry, "nested_site", site->nested_site(),
            AllocationSite::kNestedSiteOffset);
        TagObject(site->dependent_code(), "(dependent code)");
        SetInternalReference(entry, "dependent_code", site->dependent_code(),
            AllocationSite::kDependentCodeOffset);
    }

    void V8HeapExplorer::ExtractArrayBoilerplateDescriptionReferences(
        HeapEntry* entry, ArrayBoilerplateDescription value)
    {
        SetInternalReference(entry, "constant_elements", value->constant_elements(),
            ArrayBoilerplateDescription::kConstantElementsOffset);
    }

    class JSArrayBufferDataEntryAllocator : public HeapEntriesAllocator {
    public:
        JSArrayBufferDataEntryAllocator(size_t size, V8HeapExplorer* explorer)
            : size_(size)
            , explorer_(explorer)
        {
        }
        HeapEntry* AllocateEntry(HeapThing ptr) override
        {
            return explorer_->AddEntry(reinterpret_cast<Address>(ptr),
                HeapEntry::kNative, "system / JSArrayBufferData",
                size_);
        }

    private:
        size_t size_;
        V8HeapExplorer* explorer_;
    };

    void V8HeapExplorer::ExtractJSArrayBufferReferences(HeapEntry* entry,
        JSArrayBuffer buffer)
    {
        // Setup a reference to a native memory backing_store object.
        if (!buffer->backing_store())
            return;
        size_t data_size = buffer->byte_length();
        JSArrayBufferDataEntryAllocator allocator(data_size, this);
        HeapEntry* data_entry = generator_->FindOrAddEntry(buffer->backing_store(), &allocator);
        entry->SetNamedReference(HeapGraphEdge::kInternal, "backing_store",
            data_entry);
    }

    void V8HeapExplorer::ExtractJSPromiseReferences(HeapEntry* entry,
        JSPromise promise)
    {
        SetInternalReference(entry, "reactions_or_result",
            promise->reactions_or_result(),
            JSPromise::kReactionsOrResultOffset);
    }

    void V8HeapExplorer::ExtractJSGeneratorObjectReferences(
        HeapEntry* entry, JSGeneratorObject generator)
    {
        SetInternalReference(entry, "function", generator->function(),
            JSGeneratorObject::kFunctionOffset);
        SetInternalReference(entry, "context", generator->context(),
            JSGeneratorObject::kContextOffset);
        SetInternalReference(entry, "receiver", generator->receiver(),
            JSGeneratorObject::kReceiverOffset);
        SetInternalReference(entry, "parameters_and_registers",
            generator->parameters_and_registers(),
            JSGeneratorObject::kParametersAndRegistersOffset);
    }

    void V8HeapExplorer::ExtractFixedArrayReferences(HeapEntry* entry,
        FixedArray array)
    {
        for (int i = 0, l = array->length(); i < l; ++i) {
            DCHECK(!HasWeakHeapObjectTag(array->get(i)));
            SetInternalReference(entry, i, array->get(i), array->OffsetOfElementAt(i));
        }
    }

    void V8HeapExplorer::ExtractFeedbackVectorReferences(
        HeapEntry* entry, FeedbackVector feedback_vector)
    {
        MaybeObject code = feedback_vector->optimized_code_weak_or_smi();
        HeapObject code_heap_object;
        if (code->GetHeapObjectIfWeak(&code_heap_object)) {
            SetWeakReference(entry, "optimized code", code_heap_object,
                FeedbackVector::kOptimizedCodeOffset);
        }
    }

    void V8HeapExplorer::ExtractDescriptorArrayReferences(HeapEntry* entry,
        DescriptorArray array)
    {
        SetInternalReference(entry, "enum_cache", array->enum_cache(),
            DescriptorArray::kEnumCacheOffset);
        MaybeObjectSlot start = MaybeObjectSlot(array->GetDescriptorSlot(0));
        MaybeObjectSlot end = MaybeObjectSlot(
            array->GetDescriptorSlot(array->number_of_all_descriptors()));
        for (int i = 0; start + i < end; ++i) {
            MaybeObjectSlot slot = start + i;
            int offset = static_cast<int>(slot.address() - array->address());
            MaybeObject object = *slot;
            HeapObject heap_object;
            if (object->GetHeapObjectIfWeak(&heap_object)) {
                SetWeakReference(entry, i, heap_object, offset);
            } else if (object->GetHeapObjectIfStrong(&heap_object)) {
                SetInternalReference(entry, i, heap_object, offset);
            }
        }
    }

    template <typename T>
    void V8HeapExplorer::ExtractWeakArrayReferences(int header_size,
        HeapEntry* entry, T array)
    {
        for (int i = 0; i < array->length(); ++i) {
            MaybeObject object = array->Get(i);
            HeapObject heap_object;
            if (object->GetHeapObjectIfWeak(&heap_object)) {
                SetWeakReference(entry, i, heap_object, header_size + i * kTaggedSize);
            } else if (object->GetHeapObjectIfStrong(&heap_object)) {
                SetInternalReference(entry, i, heap_object,
                    header_size + i * kTaggedSize);
            }
        }
    }

    void V8HeapExplorer::ExtractPropertyReferences(JSObject js_obj,
        HeapEntry* entry)
    {
        Isolate* isolate = js_obj->GetIsolate();
        if (js_obj->HasFastProperties()) {
            DescriptorArray descs = js_obj->map()->instance_descriptors();
            int real_size = js_obj->map()->NumberOfOwnDescriptors();
            for (int i = 0; i < real_size; i++) {
                PropertyDetails details = descs->GetDetails(i);
                switch (details.location()) {
                case kField: {
                    Representation r = details.representation();
                    if (r.IsSmi() || r.IsDouble())
                        break;

                    Name k = descs->GetKey(i);
                    FieldIndex field_index = FieldIndex::ForDescriptor(js_obj->map(), i);
                    Object value = js_obj->RawFastPropertyAt(field_index);
                    int field_offset = field_index.is_inobject() ? field_index.offset() : -1;

                    SetDataOrAccessorPropertyReference(details.kind(), entry, k, value,
                        nullptr, field_offset);
                    break;
                }
                case kDescriptor:
                    SetDataOrAccessorPropertyReference(details.kind(), entry,
                        descs->GetKey(i),
                        descs->GetStrongValue(i));
                    break;
                }
            }
        } else if (js_obj->IsJSGlobalObject()) {
            // We assume that global objects can only have slow properties.
            GlobalDictionary dictionary = JSGlobalObject::cast(js_obj)->global_dictionary();
            int length = dictionary->Capacity();
            ReadOnlyRoots roots(isolate);
            for (int i = 0; i < length; ++i) {
                if (!dictionary->IsKey(roots, dictionary->KeyAt(i)))
                    continue;
                PropertyCell cell = dictionary->CellAt(i);
                Name name = cell->name();
                Object value = cell->value();
                PropertyDetails details = cell->property_details();
                SetDataOrAccessorPropertyReference(details.kind(), entry, name, value);
            }
        } else {
            NameDictionary dictionary = js_obj->property_dictionary();
            int length = dictionary->Capacity();
            ReadOnlyRoots roots(isolate);
            for (int i = 0; i < length; ++i) {
                Object k = dictionary->KeyAt(i);
                if (!dictionary->IsKey(roots, k))
                    continue;
                Object value = dictionary->ValueAt(i);
                PropertyDetails details = dictionary->DetailsAt(i);
                SetDataOrAccessorPropertyReference(details.kind(), entry, Name::cast(k),
                    value);
            }
        }
    }

    void V8HeapExplorer::ExtractAccessorPairProperty(HeapEntry* entry, Name key,
        Object callback_obj,
        int field_offset)
    {
        if (!callback_obj->IsAccessorPair())
            return;
        AccessorPair accessors = AccessorPair::cast(callback_obj);
        SetPropertyReference(entry, key, accessors, nullptr, field_offset);
        Object getter = accessors->getter();
        if (!getter->IsOddball()) {
            SetPropertyReference(entry, key, getter, "get %s");
        }
        Object setter = accessors->setter();
        if (!setter->IsOddball()) {
            SetPropertyReference(entry, key, setter, "set %s");
        }
    }

    void V8HeapExplorer::ExtractElementReferences(JSObject js_obj,
        HeapEntry* entry)
    {
        ReadOnlyRoots roots = js_obj->GetReadOnlyRoots();
        if (js_obj->HasObjectElements()) {
            FixedArray elements = FixedArray::cast(js_obj->elements());
            int length = js_obj->IsJSArray()
                ? Smi::ToInt(JSArray::cast(js_obj)->length())
                : elements->length();
            for (int i = 0; i < length; ++i) {
                if (!elements->get(i)->IsTheHole(roots)) {
                    SetElementReference(entry, i, elements->get(i));
                }
            }
        } else if (js_obj->HasDictionaryElements()) {
            NumberDictionary dictionary = js_obj->element_dictionary();
            int length = dictionary->Capacity();
            for (int i = 0; i < length; ++i) {
                Object k = dictionary->KeyAt(i);
                if (!dictionary->IsKey(roots, k))
                    continue;
                DCHECK(k->IsNumber());
                uint32_t index = static_cast<uint32_t>(k->Number());
                SetElementReference(entry, index, dictionary->ValueAt(i));
            }
        }
    }

    void V8HeapExplorer::ExtractInternalReferences(JSObject js_obj,
        HeapEntry* entry)
    {
        int length = js_obj->GetEmbedderFieldCount();
        for (int i = 0; i < length; ++i) {
            Object o = js_obj->GetEmbedderField(i);
            SetInternalReference(entry, i, o, js_obj->GetEmbedderFieldOffset(i));
        }
    }

    JSFunction V8HeapExplorer::GetConstructor(JSReceiver receiver)
    {
        Isolate* isolate = receiver->GetIsolate();
        DisallowHeapAllocation no_gc;
        HandleScope scope(isolate);
        MaybeHandle<JSFunction> maybe_constructor = JSReceiver::GetConstructor(handle(receiver, isolate));

        if (maybe_constructor.is_null())
            return JSFunction();

        return *maybe_constructor.ToHandleChecked();
    }

    String V8HeapExplorer::GetConstructorName(JSObject object)
    {
        Isolate* isolate = object->GetIsolate();
        if (object->IsJSFunction())
            return ReadOnlyRoots(isolate).closure_string();
        DisallowHeapAllocation no_gc;
        HandleScope scope(isolate);
        return *JSReceiver::GetConstructorName(handle(object, isolate));
    }

    HeapEntry* V8HeapExplorer::GetEntry(Object obj)
    {
        return obj->IsHeapObject() ? generator_->FindOrAddEntry(
                   reinterpret_cast<void*>(obj.ptr()), this)
                                   : nullptr;
    }

    class RootsReferencesExtractor : public RootVisitor {
    public:
        explicit RootsReferencesExtractor(V8HeapExplorer* explorer)
            : explorer_(explorer)
            , visiting_weak_roots_(false)
        {
        }

        void SetVisitingWeakRoots() { visiting_weak_roots_ = true; }

        void VisitRootPointer(Root root, const char* description,
            FullObjectSlot object) override
        {
            if (root == Root::kBuiltins) {
                explorer_->TagBuiltinCodeObject(Code::cast(*object), description);
            }
            explorer_->SetGcSubrootReference(root, description, visiting_weak_roots_,
                *object);
        }

        void VisitRootPointers(Root root, const char* description,
            FullObjectSlot start, FullObjectSlot end) override
        {
            for (FullObjectSlot p = start; p < end; ++p) {
                VisitRootPointer(root, description, p);
            }
        }

    private:
        V8HeapExplorer* explorer_;
        bool visiting_weak_roots_;
    };

    bool V8HeapExplorer::IterateAndExtractReferences(
        HeapSnapshotGenerator* generator)
    {
        generator_ = generator;

        // Create references to the synthetic roots.
        SetRootGcRootsReference();
        for (int root = 0; root < static_cast<int>(Root::kNumberOfRoots); root++) {
            SetGcRootsReference(static_cast<Root>(root));
        }

        // Make sure builtin code objects get their builtin tags
        // first. Otherwise a particular JSFunction object could set
        // its custom name to a generic builtin.
        RootsReferencesExtractor extractor(this);
        ReadOnlyRoots(heap_).Iterate(&extractor);
        heap_->IterateRoots(&extractor, VISIT_ONLY_STRONG);
        extractor.SetVisitingWeakRoots();
        heap_->IterateWeakGlobalHandles(&extractor);

        bool interrupted = false;

        HeapIterator iterator(heap_, HeapIterator::kFilterUnreachable);
        // Heap iteration with filtering must be finished in any case.
        for (HeapObject obj = iterator.next(); !obj.is_null();
             obj = iterator.next(), progress_->ProgressStep()) {
            if (interrupted)
                continue;

            size_t max_pointer = obj->Size() / kTaggedSize;
            if (max_pointer > visited_fields_.size()) {
                // Clear the current bits.
                std::vector<bool>().swap(visited_fields_);
                // Reallocate to right size.
                visited_fields_.resize(max_pointer, false);
            }

            HeapEntry* entry = GetEntry(obj);
            ExtractReferences(entry, obj);
            SetInternalReference(entry, "map", obj->map(), HeapObject::kMapOffset);
            // Extract unvisited fields as hidden references and restore tags
            // of visited fields.
            IndexedReferencesExtractor refs_extractor(this, obj, entry);
            obj->Iterate(&refs_extractor);

            // Ensure visited_fields_ doesn't leak to the next object.
            for (size_t i = 0; i < max_pointer; ++i) {
                DCHECK(!visited_fields_[i]);
            }

            // Extract location for specific object types
            ExtractLocation(entry, obj);

            if (!progress_->ProgressReport(false))
                interrupted = true;
        }

        generator_ = nullptr;
        return interrupted ? false : progress_->ProgressReport(true);
    }

    bool V8HeapExplorer::IsEssentialObject(Object object)
    {
        ReadOnlyRoots roots(heap_);
        return object->IsHeapObject() && !object->IsOddball() && object != roots.empty_byte_array() && object != roots.empty_fixed_array() && object != roots.empty_weak_fixed_array() && object != roots.empty_descriptor_array() && object != roots.fixed_array_map() && object != roots.cell_map() && object != roots.global_property_cell_map() && object != roots.shared_function_info_map() && object != roots.free_space_map() && object != roots.one_pointer_filler_map() && object != roots.two_pointer_filler_map();
    }

    bool V8HeapExplorer::IsEssentialHiddenReference(Object parent,
        int field_offset)
    {
        if (parent->IsAllocationSite() && field_offset == AllocationSite::kWeakNextOffset)
            return false;
        if (parent->IsCodeDataContainer() && field_offset == CodeDataContainer::kNextCodeLinkOffset)
            return false;
        if (parent->IsContext() && field_offset == Context::OffsetOfElementAt(Context::NEXT_CONTEXT_LINK))
            return false;
        return true;
    }

    void V8HeapExplorer::SetContextReference(HeapEntry* parent_entry,
        String reference_name,
        Object child_obj, int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        parent_entry->SetNamedReference(HeapGraphEdge::kContextVariable,
            names_->GetName(reference_name), child_entry);
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::MarkVisitedField(int offset)
    {
        if (offset < 0)
            return;
        int index = offset / kTaggedSize;
        DCHECK(!visited_fields_[index]);
        visited_fields_[index] = true;
    }

    void V8HeapExplorer::SetNativeBindReference(HeapEntry* parent_entry,
        const char* reference_name,
        Object child_obj)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        parent_entry->SetNamedReference(HeapGraphEdge::kShortcut, reference_name,
            child_entry);
    }

    void V8HeapExplorer::SetElementReference(HeapEntry* parent_entry, int index,
        Object child_obj)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        parent_entry->SetIndexedReference(HeapGraphEdge::kElement, index,
            child_entry);
    }

    void V8HeapExplorer::SetInternalReference(HeapEntry* parent_entry,
        const char* reference_name,
        Object child_obj, int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        if (IsEssentialObject(child_obj)) {
            parent_entry->SetNamedReference(HeapGraphEdge::kInternal, reference_name,
                child_entry);
        }
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::SetInternalReference(HeapEntry* parent_entry, int index,
        Object child_obj, int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        if (IsEssentialObject(child_obj)) {
            parent_entry->SetNamedReference(HeapGraphEdge::kInternal,
                names_->GetName(index), child_entry);
        }
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::SetHiddenReference(HeapObject parent_obj,
        HeapEntry* parent_entry, int index,
        Object child_obj, int field_offset)
    {
        DCHECK_EQ(parent_entry, GetEntry(parent_obj));
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry != nullptr && IsEssentialObject(child_obj) && IsEssentialHiddenReference(parent_obj, field_offset)) {
            parent_entry->SetIndexedReference(HeapGraphEdge::kHidden, index,
                child_entry);
        }
    }

    void V8HeapExplorer::SetWeakReference(HeapEntry* parent_entry,
        const char* reference_name,
        Object child_obj, int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        if (IsEssentialObject(child_obj)) {
            parent_entry->SetNamedReference(HeapGraphEdge::kWeak, reference_name,
                child_entry);
        }
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::SetWeakReference(HeapEntry* parent_entry, int index,
        Object child_obj, int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        if (IsEssentialObject(child_obj)) {
            parent_entry->SetNamedReference(
                HeapGraphEdge::kWeak, names_->GetFormatted("%d", index), child_entry);
        }
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::SetDataOrAccessorPropertyReference(
        PropertyKind kind, HeapEntry* parent_entry, Name reference_name,
        Object child_obj, const char* name_format_string, int field_offset)
    {
        if (kind == kAccessor) {
            ExtractAccessorPairProperty(parent_entry, reference_name, child_obj,
                field_offset);
        } else {
            SetPropertyReference(parent_entry, reference_name, child_obj,
                name_format_string, field_offset);
        }
    }

    void V8HeapExplorer::SetPropertyReference(HeapEntry* parent_entry,
        Name reference_name, Object child_obj,
        const char* name_format_string,
        int field_offset)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        HeapGraphEdge::Type type = reference_name->IsSymbol() || String::cast(reference_name)->length() > 0
            ? HeapGraphEdge::kProperty
            : HeapGraphEdge::kInternal;
        const char* name = name_format_string != nullptr && reference_name->IsString()
            ? names_->GetFormatted(
                name_format_string,
                String::cast(reference_name)
                    ->ToCString(DISALLOW_NULLS, ROBUST_STRING_TRAVERSAL)
                    .get())
            : names_->GetName(reference_name);

        parent_entry->SetNamedReference(type, name, child_entry);
        MarkVisitedField(field_offset);
    }

    void V8HeapExplorer::SetRootGcRootsReference()
    {
        snapshot_->root()->SetIndexedAutoIndexReference(HeapGraphEdge::kElement,
            snapshot_->gc_roots());
    }

    void V8HeapExplorer::SetUserGlobalReference(Object child_obj)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        DCHECK_NOT_NULL(child_entry);
        snapshot_->root()->SetNamedAutoIndexReference(HeapGraphEdge::kShortcut,
            nullptr, child_entry, names_);
    }

    void V8HeapExplorer::SetGcRootsReference(Root root)
    {
        snapshot_->gc_roots()->SetIndexedAutoIndexReference(
            HeapGraphEdge::kElement, snapshot_->gc_subroot(root));
    }

    void V8HeapExplorer::SetGcSubrootReference(Root root, const char* description,
        bool is_weak, Object child_obj)
    {
        HeapEntry* child_entry = GetEntry(child_obj);
        if (child_entry == nullptr)
            return;
        const char* name = GetStrongGcSubrootName(child_obj);
        HeapGraphEdge::Type edge_type = is_weak ? HeapGraphEdge::kWeak : HeapGraphEdge::kInternal;
        if (name != nullptr) {
            snapshot_->gc_subroot(root)->SetNamedReference(edge_type, name,
                child_entry);
        } else {
            snapshot_->gc_subroot(root)->SetNamedAutoIndexReference(
                edge_type, description, child_entry, names_);
        }

        // For full heap snapshots we do not emit user roots but rather rely on
        // regular GC roots to retain objects.
        if (FLAG_raw_heap_snapshots)
            return;

        // Add a shortcut to JS global object reference at snapshot root.
        // That allows the user to easily find global objects. They are
        // also used as starting points in distance calculations.
        if (is_weak || !child_obj->IsNativeContext())
            return;

        JSGlobalObject global = Context::cast(child_obj)->global_object();
        if (!global->IsJSGlobalObject())
            return;

        if (!user_roots_.insert(global).second)
            return;

        SetUserGlobalReference(global);
    }

    const char* V8HeapExplorer::GetStrongGcSubrootName(Object object)
    {
        if (strong_gc_subroot_names_.empty()) {
            Isolate* isolate = Isolate::FromHeap(heap_);
            for (RootIndex root_index = RootIndex::kFirstStrongOrReadOnlyRoot;
                 root_index <= RootIndex::kLastStrongOrReadOnlyRoot; ++root_index) {
                const char* name = RootsTable::name(root_index);
                strong_gc_subroot_names_.emplace(isolate->root(root_index), name);
            }
            CHECK(!strong_gc_subroot_names_.empty());
        }
        auto it = strong_gc_subroot_names_.find(object);
        return it != strong_gc_subroot_names_.end() ? it->second : nullptr;
    }

    void V8HeapExplorer::TagObject(Object obj, const char* tag)
    {
        if (IsEssentialObject(obj)) {
            HeapEntry* entry = GetEntry(obj);
            if (entry->name()[0] == '\0') {
                entry->set_name(tag);
            }
        }
    }

    class GlobalObjectsEnumerator : public RootVisitor {
    public:
        void VisitRootPointers(Root root, const char* description,
            FullObjectSlot start, FullObjectSlot end) override
        {
            for (FullObjectSlot p = start; p < end; ++p) {
                if (!(*p)->IsNativeContext())
                    continue;
                JSObject proxy = Context::cast(*p)->global_proxy();
                if (!proxy->IsJSGlobalProxy())
                    continue;
                Object global = proxy->map()->prototype();
                if (!global->IsJSGlobalObject())
                    continue;
                objects_.push_back(Handle<JSGlobalObject>(JSGlobalObject::cast(global),
                    proxy->GetIsolate()));
            }
        }
        int count() const { return static_cast<int>(objects_.size()); }
        Handle<JSGlobalObject>& at(int i) { return objects_[i]; }

    private:
        std::vector<Handle<JSGlobalObject>> objects_;
    };

    // Modifies heap. Must not be run during heap traversal.
    void V8HeapExplorer::TagGlobalObjects()
    {
        Isolate* isolate = Isolate::FromHeap(heap_);
        HandleScope scope(isolate);
        GlobalObjectsEnumerator enumerator;
        isolate->global_handles()->IterateAllRoots(&enumerator);
        std::vector<const char*> urls(enumerator.count());
        for (int i = 0, l = enumerator.count(); i < l; ++i) {
            urls[i] = global_object_name_resolver_
                ? global_object_name_resolver_->GetName(Utils::ToLocal(
                    Handle<JSObject>::cast(enumerator.at(i))))
                : nullptr;
        }

        DisallowHeapAllocation no_allocation;
        for (int i = 0, l = enumerator.count(); i < l; ++i) {
            if (urls[i])
                objects_tags_.emplace(*enumerator.at(i), urls[i]);
        }
    }

    class EmbedderGraphImpl : public EmbedderGraph {
    public:
        struct Edge {
            Node* from;
            Node* to;
            const char* name;
        };

        class V8NodeImpl : public Node {
        public:
            explicit V8NodeImpl(Object object)
                : object_(object)
            {
            }
            Object GetObject() { return object_; }

            // Node overrides.
            bool IsEmbedderNode() override { return false; }
            const char* Name() override
            {
                // The name should be retrieved via GetObject().
                UNREACHABLE();
                return "";
            }
            size_t SizeInBytes() override
            {
                // The size should be retrieved via GetObject().
                UNREACHABLE();
                return 0;
            }

        private:
            Object object_;
        };

        Node* V8Node(const v8::Local<v8::Value>& value) final
        {
            Handle<Object> object = v8::Utils::OpenHandle(*value);
            DCHECK(!object.is_null());
            return AddNode(std::unique_ptr<Node>(new V8NodeImpl(*object)));
        }

        Node* AddNode(std::unique_ptr<Node> node) final
        {
            Node* result = node.get();
            nodes_.push_back(std::move(node));
            return result;
        }

        void AddEdge(Node* from, Node* to, const char* name) final
        {
            edges_.push_back({ from, to, name });
        }

        const std::vector<std::unique_ptr<Node>>& nodes() { return nodes_; }
        const std::vector<Edge>& edges() { return edges_; }

    private:
        std::vector<std::unique_ptr<Node>> nodes_;
        std::vector<Edge> edges_;
    };

    class EmbedderGraphEntriesAllocator : public HeapEntriesAllocator {
    public:
        explicit EmbedderGraphEntriesAllocator(HeapSnapshot* snapshot)
            : snapshot_(snapshot)
            , names_(snapshot_->profiler()->names())
            , heap_object_map_(snapshot_->profiler()->heap_object_map())
        {
        }
        HeapEntry* AllocateEntry(HeapThing ptr) override;

    private:
        HeapSnapshot* snapshot_;
        StringsStorage* names_;
        HeapObjectsMap* heap_object_map_;
    };

    namespace {

        const char* EmbedderGraphNodeName(StringsStorage* names,
            EmbedderGraphImpl::Node* node)
        {
            const char* prefix = node->NamePrefix();
            return prefix ? names->GetFormatted("%s %s", prefix, node->Name())
                          : names->GetCopy(node->Name());
        }

        HeapEntry::Type EmbedderGraphNodeType(EmbedderGraphImpl::Node* node)
        {
            return node->IsRootNode() ? HeapEntry::kSynthetic : HeapEntry::kNative;
        }

        // Merges the names of an embedder node and its wrapper node.
        // If the wrapper node name contains a tag suffix (part after '/') then the
        // result is the embedder node name concatenated with the tag suffix.
        // Otherwise, the result is the embedder node name.
        const char* MergeNames(StringsStorage* names, const char* embedder_name,
            const char* wrapper_name)
        {
            const char* suffix = strchr(wrapper_name, '/');
            return suffix ? names->GetFormatted("%s %s", embedder_name, suffix)
                          : embedder_name;
        }

    } // anonymous namespace

    HeapEntry* EmbedderGraphEntriesAllocator::AllocateEntry(HeapThing ptr)
    {
        EmbedderGraphImpl::Node* node = reinterpret_cast<EmbedderGraphImpl::Node*>(ptr);
        DCHECK(node->IsEmbedderNode());
        size_t size = node->SizeInBytes();
        return snapshot_->AddEntry(
            EmbedderGraphNodeType(node), EmbedderGraphNodeName(names_, node),
            static_cast<SnapshotObjectId>(reinterpret_cast<uintptr_t>(node) << 1),
            static_cast<int>(size), 0);
    }

    NativeObjectsExplorer::NativeObjectsExplorer(
        HeapSnapshot* snapshot, SnapshottingProgressReportingInterface* progress)
        : isolate_(
            Isolate::FromHeap(snapshot->profiler()->heap_object_map()->heap()))
        , snapshot_(snapshot)
        , names_(snapshot_->profiler()->names())
        , embedder_graph_entries_allocator_(
              new EmbedderGraphEntriesAllocator(snapshot))
    {
    }

    HeapEntry* NativeObjectsExplorer::EntryForEmbedderGraphNode(
        EmbedderGraphImpl::Node* node)
    {
        EmbedderGraphImpl::Node* wrapper = node->WrapperNode();
        if (wrapper) {
            node = wrapper;
        }
        if (node->IsEmbedderNode()) {
            return generator_->FindOrAddEntry(node,
                embedder_graph_entries_allocator_.get());
        } else {
            EmbedderGraphImpl::V8NodeImpl* v8_node = static_cast<EmbedderGraphImpl::V8NodeImpl*>(node);
            Object object = v8_node->GetObject();
            if (object->IsSmi())
                return nullptr;
            return generator_->FindEntry(
                reinterpret_cast<void*>(Object::cast(object).ptr()));
        }
    }

    bool NativeObjectsExplorer::IterateAndExtractReferences(
        HeapSnapshotGenerator* generator)
    {
        generator_ = generator;

        if (FLAG_heap_profiler_use_embedder_graph && snapshot_->profiler()->HasBuildEmbedderGraphCallback()) {
            v8::HandleScope scope(reinterpret_cast<v8::Isolate*>(isolate_));
            DisallowHeapAllocation no_allocation;
            EmbedderGraphImpl graph;
            snapshot_->profiler()->BuildEmbedderGraph(isolate_, &graph);
            for (const auto& node : graph.nodes()) {
                if (node->IsRootNode()) {
                    snapshot_->root()->SetIndexedAutoIndexReference(
                        HeapGraphEdge::kElement, EntryForEmbedderGraphNode(node.get()));
                }
                // Adjust the name and the type of the V8 wrapper node.
                auto wrapper = node->WrapperNode();
                if (wrapper) {
                    HeapEntry* wrapper_entry = EntryForEmbedderGraphNode(wrapper);
                    wrapper_entry->set_name(
                        MergeNames(names_, EmbedderGraphNodeName(names_, node.get()),
                            wrapper_entry->name()));
                    wrapper_entry->set_type(EmbedderGraphNodeType(node.get()));
                }
            }
            // Fill edges of the graph.
            for (const auto& edge : graph.edges()) {
                HeapEntry* from = EntryForEmbedderGraphNode(edge.from);
                // |from| and |to| can be nullptr if the corresponding node is a V8 node
                // pointing to a Smi.
                if (!from)
                    continue;
                HeapEntry* to = EntryForEmbedderGraphNode(edge.to);
                if (!to)
                    continue;
                if (edge.name == nullptr) {
                    from->SetIndexedAutoIndexReference(HeapGraphEdge::kElement, to);
                } else {
                    from->SetNamedReference(HeapGraphEdge::kInternal,
                        names_->GetCopy(edge.name), to);
                }
            }
        }
        generator_ = nullptr;
        return true;
    }

    HeapSnapshotGenerator::HeapSnapshotGenerator(
        HeapSnapshot* snapshot,
        v8::ActivityControl* control,
        v8::HeapProfiler::ObjectNameResolver* resolver,
        Heap* heap)
        : snapshot_(snapshot)
        , control_(control)
        , v8_heap_explorer_(snapshot_, this, resolver)
        , dom_explorer_(snapshot_, this)
        , heap_(heap)
    {
    }

    namespace {
        class NullContextScope {
        public:
            explicit NullContextScope(Isolate* isolate)
                : isolate_(isolate)
                , prev_(isolate->context())
            {
                isolate_->set_context(Context());
            }
            ~NullContextScope() { isolate_->set_context(prev_); }

        private:
            Isolate* isolate_;
            Context prev_;
        };
    } //  namespace

    bool HeapSnapshotGenerator::GenerateSnapshot()
    {
        v8_heap_explorer_.TagGlobalObjects();

        // TODO(1562) Profiler assumes that any object that is in the heap after
        // full GC is reachable from the root when computing dominators.
        // This is not true for weakly reachable objects.
        // As a temporary solution we call GC twice.
        heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
            GarbageCollectionReason::kHeapProfiler);
        heap_->PreciseCollectAllGarbage(Heap::kNoGCFlags,
            GarbageCollectionReason::kHeapProfiler);

        NullContextScope null_context_scope(Isolate::FromHeap(heap_));

#ifdef VERIFY_HEAP
        Heap* debug_heap = heap_;
        if (FLAG_verify_heap) {
            debug_heap->Verify();
        }
#endif

        InitProgressCounter();

#ifdef VERIFY_HEAP
        if (FLAG_verify_heap) {
            debug_heap->Verify();
        }
#endif

        snapshot_->AddSyntheticRootEntries();

        if (!FillReferences())
            return false;

        snapshot_->FillChildren();
        snapshot_->RememberLastJSObjectId();

        progress_counter_ = progress_total_;
        if (!ProgressReport(true))
            return false;
        return true;
    }

    void HeapSnapshotGenerator::ProgressStep()
    {
        ++progress_counter_;
    }

    bool HeapSnapshotGenerator::ProgressReport(bool force)
    {
        const int kProgressReportGranularity = 10000;
        if (control_ != nullptr && (force || progress_counter_ % kProgressReportGranularity == 0)) {
            return control_->ReportProgressValue(progress_counter_, progress_total_) == v8::ActivityControl::kContinue;
        }
        return true;
    }

    void HeapSnapshotGenerator::InitProgressCounter()
    {
        if (control_ == nullptr)
            return;
        // The +1 ensures that intermediate ProgressReport calls will never signal
        // that the work is finished (i.e. progress_counter_ == progress_total_).
        // Only the forced ProgressReport() at the end of GenerateSnapshot()
        // should signal that the work is finished because signalling finished twice
        // breaks the DevTools frontend.
        progress_total_ = v8_heap_explorer_.EstimateObjectsCount() + 1;
        progress_counter_ = 0;
    }

    bool HeapSnapshotGenerator::FillReferences()
    {
        return v8_heap_explorer_.IterateAndExtractReferences(this) && dom_explorer_.IterateAndExtractReferences(this);
    }

    template <int bytes>
    struct MaxDecimalDigitsIn;
    template <>
    struct MaxDecimalDigitsIn<4> {
        static const int kSigned = 11;
        static const int kUnsigned = 10;
    };
    template <>
    struct MaxDecimalDigitsIn<8> {
        static const int kSigned = 20;
        static const int kUnsigned = 20;
    };

    class OutputStreamWriter {
    public:
        explicit OutputStreamWriter(v8::OutputStream* stream)
            : stream_(stream)
            , chunk_size_(stream->GetChunkSize())
            , chunk_(chunk_size_)
            , chunk_pos_(0)
            , aborted_(false)
        {
            DCHECK_GT(chunk_size_, 0);
        }
        bool aborted() { return aborted_; }
        void AddCharacter(char c)
        {
            DCHECK_NE(c, '\0');
            DCHECK(chunk_pos_ < chunk_size_);
            chunk_[chunk_pos_++] = c;
            MaybeWriteChunk();
        }
        void AddString(const char* s)
        {
            AddSubstring(s, StrLength(s));
        }
        void AddSubstring(const char* s, int n)
        {
            if (n <= 0)
                return;
            DCHECK(static_cast<size_t>(n) <= strlen(s));
            const char* s_end = s + n;
            while (s < s_end) {
                int s_chunk_size = Min(chunk_size_ - chunk_pos_, static_cast<int>(s_end - s));
                DCHECK_GT(s_chunk_size, 0);
                MemCopy(chunk_.start() + chunk_pos_, s, s_chunk_size);
                s += s_chunk_size;
                chunk_pos_ += s_chunk_size;
                MaybeWriteChunk();
            }
        }
        void AddNumber(unsigned n) { AddNumberImpl<unsigned>(n, "%u"); }
        void Finalize()
        {
            if (aborted_)
                return;
            DCHECK(chunk_pos_ < chunk_size_);
            if (chunk_pos_ != 0) {
                WriteChunk();
            }
            stream_->EndOfStream();
        }

    private:
        template <typename T>
        void AddNumberImpl(T n, const char* format)
        {
            // Buffer for the longest value plus trailing \0
            static const int kMaxNumberSize = MaxDecimalDigitsIn<sizeof(T)>::kUnsigned + 1;
            if (chunk_size_ - chunk_pos_ >= kMaxNumberSize) {
                int result = SNPrintF(
                    chunk_.SubVector(chunk_pos_, chunk_size_), format, n);
                DCHECK_NE(result, -1);
                chunk_pos_ += result;
                MaybeWriteChunk();
            } else {
                EmbeddedVector<char, kMaxNumberSize> buffer;
                int result = SNPrintF(buffer, format, n);
                USE(result);
                DCHECK_NE(result, -1);
                AddString(buffer.start());
            }
        }
        void MaybeWriteChunk()
        {
            DCHECK(chunk_pos_ <= chunk_size_);
            if (chunk_pos_ == chunk_size_) {
                WriteChunk();
            }
        }
        void WriteChunk()
        {
            if (aborted_)
                return;
            if (stream_->WriteAsciiChunk(chunk_.start(), chunk_pos_) == v8::OutputStream::kAbort)
                aborted_ = true;
            chunk_pos_ = 0;
        }

        v8::OutputStream* stream_;
        int chunk_size_;
        ScopedVector<char> chunk_;
        int chunk_pos_;
        bool aborted_;
    };

    // type, name|index, to_node.
    const int HeapSnapshotJSONSerializer::kEdgeFieldsCount = 3;
    // type, name, id, self_size, edge_count, trace_node_id.
    const int HeapSnapshotJSONSerializer::kNodeFieldsCount = 6;

    void HeapSnapshotJSONSerializer::Serialize(v8::OutputStream* stream)
    {
        if (AllocationTracker* allocation_tracker = snapshot_->profiler()->allocation_tracker()) {
            allocation_tracker->PrepareForSerialization();
        }
        DCHECK_NULL(writer_);
        writer_ = new OutputStreamWriter(stream);
        SerializeImpl();
        delete writer_;
        writer_ = nullptr;
    }

    void HeapSnapshotJSONSerializer::SerializeImpl()
    {
        DCHECK_EQ(0, snapshot_->root()->index());
        writer_->AddCharacter('{');
        writer_->AddString("\"snapshot\":{");
        SerializeSnapshot();
        if (writer_->aborted())
            return;
        writer_->AddString("},\n");
        writer_->AddString("\"nodes\":[");
        SerializeNodes();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");
        writer_->AddString("\"edges\":[");
        SerializeEdges();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");

        writer_->AddString("\"trace_function_infos\":[");
        SerializeTraceNodeInfos();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");
        writer_->AddString("\"trace_tree\":[");
        SerializeTraceTree();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");

        writer_->AddString("\"samples\":[");
        SerializeSamples();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");

        writer_->AddString("\"locations\":[");
        SerializeLocations();
        if (writer_->aborted())
            return;
        writer_->AddString("],\n");

        writer_->AddString("\"strings\":[");
        SerializeStrings();
        if (writer_->aborted())
            return;
        writer_->AddCharacter(']');
        writer_->AddCharacter('}');
        writer_->Finalize();
    }

    int HeapSnapshotJSONSerializer::GetStringId(const char* s)
    {
        base::HashMap::Entry* cache_entry = strings_.LookupOrInsert(const_cast<char*>(s), StringHash(s));
        if (cache_entry->value == nullptr) {
            cache_entry->value = reinterpret_cast<void*>(next_string_id_++);
        }
        return static_cast<int>(reinterpret_cast<intptr_t>(cache_entry->value));
    }

    namespace {

        template <size_t size>
        struct ToUnsigned;

        template <>
        struct ToUnsigned<4> {
            typedef uint32_t Type;
        };

        template <>
        struct ToUnsigned<8> {
            typedef uint64_t Type;
        };

    } // namespace

    template <typename T>
    static int utoa_impl(T value, const Vector<char>& buffer, int buffer_pos)
    {
        STATIC_ASSERT(static_cast<T>(-1) > 0); // Check that T is unsigned
        int number_of_digits = 0;
        T t = value;
        do {
            ++number_of_digits;
        } while (t /= 10);

        buffer_pos += number_of_digits;
        int result = buffer_pos;
        do {
            int last_digit = static_cast<int>(value % 10);
            buffer[--buffer_pos] = '0' + last_digit;
            value /= 10;
        } while (value);
        return result;
    }

    template <typename T>
    static int utoa(T value, const Vector<char>& buffer, int buffer_pos)
    {
        typename ToUnsigned<sizeof(value)>::Type unsigned_value = value;
        STATIC_ASSERT(sizeof(value) == sizeof(unsigned_value));
        return utoa_impl(unsigned_value, buffer, buffer_pos);
    }

    void HeapSnapshotJSONSerializer::SerializeEdge(HeapGraphEdge* edge,
        bool first_edge)
    {
        // The buffer needs space for 3 unsigned ints, 3 commas, \n and \0
        static const int kBufferSize = MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned * 3 + 3 + 2; // NOLINT
        EmbeddedVector<char, kBufferSize> buffer;
        int edge_name_or_index = edge->type() == HeapGraphEdge::kElement
                || edge->type() == HeapGraphEdge::kHidden
            ? edge->index()
            : GetStringId(edge->name());
        int buffer_pos = 0;
        if (!first_edge) {
            buffer[buffer_pos++] = ',';
        }
        buffer_pos = utoa(edge->type(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(edge_name_or_index, buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(to_node_index(edge->to()), buffer, buffer_pos);
        buffer[buffer_pos++] = '\n';
        buffer[buffer_pos++] = '\0';
        writer_->AddString(buffer.start());
    }

    void HeapSnapshotJSONSerializer::SerializeEdges()
    {
        std::vector<HeapGraphEdge*>& edges = snapshot_->children();
        for (size_t i = 0; i < edges.size(); ++i) {
            DCHECK(i == 0 || edges[i - 1]->from()->index() <= edges[i]->from()->index());
            SerializeEdge(edges[i], i == 0);
            if (writer_->aborted())
                return;
        }
    }

    void HeapSnapshotJSONSerializer::SerializeNode(const HeapEntry* entry)
    {
        // The buffer needs space for 4 unsigned ints, 1 size_t, 5 commas, \n and \0
        static const int kBufferSize = 5 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned // NOLINT
            + MaxDecimalDigitsIn<sizeof(size_t)>::kUnsigned // NOLINT
            + 6 + 1 + 1;
        EmbeddedVector<char, kBufferSize> buffer;
        int buffer_pos = 0;
        if (to_node_index(entry) != 0) {
            buffer[buffer_pos++] = ',';
        }
        buffer_pos = utoa(entry->type(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(GetStringId(entry->name()), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(entry->id(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(entry->self_size(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(entry->children_count(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(entry->trace_node_id(), buffer, buffer_pos);
        buffer[buffer_pos++] = '\n';
        buffer[buffer_pos++] = '\0';
        writer_->AddString(buffer.start());
    }

    void HeapSnapshotJSONSerializer::SerializeNodes()
    {
        const std::deque<HeapEntry>& entries = snapshot_->entries();
        for (const HeapEntry& entry : entries) {
            SerializeNode(&entry);
            if (writer_->aborted())
                return;
        }
    }

    void HeapSnapshotJSONSerializer::SerializeSnapshot()
    {
        writer_->AddString("\"meta\":");
        // The object describing node serialization layout.
        // We use a set of macros to improve readability.

// clang-format on
#define JSON_A(s) "[" s "]"
#define JSON_O(s) "{" s "}"
#define JSON_S(s) "\"" s "\""
        writer_->AddString(JSON_O(
            JSON_S("node_fields") ":" JSON_A(
                JSON_S("type") "," JSON_S("name") "," JSON_S("id") "," JSON_S("self_size") "," JSON_S("edge_count") "," JSON_S("trace_node_id")) "," JSON_S("node_types") ":" JSON_A(JSON_A(JSON_S("hidden") "," JSON_S("array") "," JSON_S("string") "," JSON_S("object") "," JSON_S("code") "," JSON_S("closure") "," JSON_S("regexp") "," JSON_S("number") "," JSON_S("native") "," JSON_S("synthetic") "," JSON_S("concatenated string") "," JSON_S("sliced string") "," JSON_S("symbol") "," JSON_S("bigint")) "," JSON_S("string") "," JSON_S("number") "," JSON_S("number") "," JSON_S("number") "," JSON_S("number") "," JSON_S("number")) "," JSON_S("edge_fields") ":" JSON_A(JSON_S("type") "," JSON_S("name_or_index") "," JSON_S("to_node")) "," JSON_S("edge_types") ":" JSON_A(JSON_A(JSON_S("context") "," JSON_S("element") "," JSON_S("property") "," JSON_S("internal") "," JSON_S("hidden") "," JSON_S("shortcut") "," JSON_S("weak")) "," JSON_S("string_or_number") "," JSON_S("node")) "," JSON_S("trace_function_info_fields") ":" JSON_A(JSON_S("function_id") "," JSON_S("name") "," JSON_S("script_name") "," JSON_S("script_id") "," JSON_S("line") "," JSON_S("column")) "," JSON_S("trace_node_fields") ":" JSON_A(JSON_S("id") "," JSON_S("function_info_index") "," JSON_S("count") "," JSON_S("size") "," JSON_S("children")) "," JSON_S("sample_fields") ":" JSON_A(JSON_S("timestamp_us") "," JSON_S("last_assigned_id")) "," JSON_S("location_fields") ":" JSON_A(JSON_S("object_index") "," JSON_S("script_id") "," JSON_S("line") "," JSON_S("column"))));
// clang-format on
#undef JSON_S
#undef JSON_O
#undef JSON_A
        writer_->AddString(",\"node_count\":");
        writer_->AddNumber(static_cast<unsigned>(snapshot_->entries().size()));
        writer_->AddString(",\"edge_count\":");
        writer_->AddNumber(static_cast<double>(snapshot_->edges().size()));
        writer_->AddString(",\"trace_function_count\":");
        uint32_t count = 0;
        AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
        if (tracker) {
            count = static_cast<uint32_t>(tracker->function_info_list().size());
        }
        writer_->AddNumber(count);
    }

    static void WriteUChar(OutputStreamWriter* w, unibrow::uchar u)
    {
        static const char hex_chars[] = "0123456789ABCDEF";
        w->AddString("\\u");
        w->AddCharacter(hex_chars[(u >> 12) & 0xF]);
        w->AddCharacter(hex_chars[(u >> 8) & 0xF]);
        w->AddCharacter(hex_chars[(u >> 4) & 0xF]);
        w->AddCharacter(hex_chars[u & 0xF]);
    }

    void HeapSnapshotJSONSerializer::SerializeTraceTree()
    {
        AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
        if (!tracker)
            return;
        AllocationTraceTree* traces = tracker->trace_tree();
        SerializeTraceNode(traces->root());
    }

    void HeapSnapshotJSONSerializer::SerializeTraceNode(AllocationTraceNode* node)
    {
        // The buffer needs space for 4 unsigned ints, 4 commas, [ and \0
        const int kBufferSize = 4 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned // NOLINT
            + 4 + 1 + 1;
        EmbeddedVector<char, kBufferSize> buffer;
        int buffer_pos = 0;
        buffer_pos = utoa(node->id(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(node->function_info_index(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(node->allocation_count(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(node->allocation_size(), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer[buffer_pos++] = '[';
        buffer[buffer_pos++] = '\0';
        writer_->AddString(buffer.start());

        int i = 0;
        for (AllocationTraceNode* child : node->children()) {
            if (i++ > 0) {
                writer_->AddCharacter(',');
            }
            SerializeTraceNode(child);
        }
        writer_->AddCharacter(']');
    }

    // 0-based position is converted to 1-based during the serialization.
    static int SerializePosition(int position, const Vector<char>& buffer,
        int buffer_pos)
    {
        if (position == -1) {
            buffer[buffer_pos++] = '0';
        } else {
            DCHECK_GE(position, 0);
            buffer_pos = utoa(static_cast<unsigned>(position + 1), buffer, buffer_pos);
        }
        return buffer_pos;
    }

    void HeapSnapshotJSONSerializer::SerializeTraceNodeInfos()
    {
        AllocationTracker* tracker = snapshot_->profiler()->allocation_tracker();
        if (!tracker)
            return;
        // The buffer needs space for 6 unsigned ints, 6 commas, \n and \0
        const int kBufferSize = 6 * MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned // NOLINT
            + 6 + 1 + 1;
        EmbeddedVector<char, kBufferSize> buffer;
        int i = 0;
        for (AllocationTracker::FunctionInfo* info : tracker->function_info_list()) {
            int buffer_pos = 0;
            if (i++ > 0) {
                buffer[buffer_pos++] = ',';
            }
            buffer_pos = utoa(info->function_id, buffer, buffer_pos);
            buffer[buffer_pos++] = ',';
            buffer_pos = utoa(GetStringId(info->name), buffer, buffer_pos);
            buffer[buffer_pos++] = ',';
            buffer_pos = utoa(GetStringId(info->script_name), buffer, buffer_pos);
            buffer[buffer_pos++] = ',';
            // The cast is safe because script id is a non-negative Smi.
            buffer_pos = utoa(static_cast<unsigned>(info->script_id), buffer,
                buffer_pos);
            buffer[buffer_pos++] = ',';
            buffer_pos = SerializePosition(info->line, buffer, buffer_pos);
            buffer[buffer_pos++] = ',';
            buffer_pos = SerializePosition(info->column, buffer, buffer_pos);
            buffer[buffer_pos++] = '\n';
            buffer[buffer_pos++] = '\0';
            writer_->AddString(buffer.start());
        }
    }

    void HeapSnapshotJSONSerializer::SerializeSamples()
    {
        const std::vector<HeapObjectsMap::TimeInterval>& samples = snapshot_->profiler()->heap_object_map()->samples();
        if (samples.empty())
            return;
        base::TimeTicks start_time = samples[0].timestamp;
        // The buffer needs space for 2 unsigned ints, 2 commas, \n and \0
        const int kBufferSize = MaxDecimalDigitsIn<sizeof(
                                    base::TimeDelta().InMicroseconds())>::kUnsigned
            + MaxDecimalDigitsIn<sizeof(samples[0].id)>::kUnsigned + 2 + 1 + 1;
        EmbeddedVector<char, kBufferSize> buffer;
        int i = 0;
        for (const HeapObjectsMap::TimeInterval& sample : samples) {
            int buffer_pos = 0;
            if (i++ > 0) {
                buffer[buffer_pos++] = ',';
            }
            base::TimeDelta time_delta = sample.timestamp - start_time;
            buffer_pos = utoa(time_delta.InMicroseconds(), buffer, buffer_pos);
            buffer[buffer_pos++] = ',';
            buffer_pos = utoa(sample.last_assigned_id(), buffer, buffer_pos);
            buffer[buffer_pos++] = '\n';
            buffer[buffer_pos++] = '\0';
            writer_->AddString(buffer.start());
        }
    }

    void HeapSnapshotJSONSerializer::SerializeString(const unsigned char* s)
    {
        writer_->AddCharacter('\n');
        writer_->AddCharacter('\"');
        for (; *s != '\0'; ++s) {
            switch (*s) {
            case '\b':
                writer_->AddString("\\b");
                continue;
            case '\f':
                writer_->AddString("\\f");
                continue;
            case '\n':
                writer_->AddString("\\n");
                continue;
            case '\r':
                writer_->AddString("\\r");
                continue;
            case '\t':
                writer_->AddString("\\t");
                continue;
            case '\"':
            case '\\':
                writer_->AddCharacter('\\');
                writer_->AddCharacter(*s);
                continue;
            default:
                if (*s > 31 && *s < 128) {
                    writer_->AddCharacter(*s);
                } else if (*s <= 31) {
                    // Special character with no dedicated literal.
                    WriteUChar(writer_, *s);
                } else {
                    // Convert UTF-8 into \u UTF-16 literal.
                    size_t length = 1, cursor = 0;
                    for (; length <= 4 && *(s + length) != '\0'; ++length) { }
                    unibrow::uchar c = unibrow::Utf8::CalculateValue(s, length, &cursor);
                    if (c != unibrow::Utf8::kBadChar) {
                        WriteUChar(writer_, c);
                        DCHECK_NE(cursor, 0);
                        s += cursor - 1;
                    } else {
                        writer_->AddCharacter('?');
                    }
                }
            }
        }
        writer_->AddCharacter('\"');
    }

    void HeapSnapshotJSONSerializer::SerializeStrings()
    {
        ScopedVector<const unsigned char*> sorted_strings(
            strings_.occupancy() + 1);
        for (base::HashMap::Entry* entry = strings_.Start(); entry != nullptr;
             entry = strings_.Next(entry)) {
            int index = static_cast<int>(reinterpret_cast<uintptr_t>(entry->value));
            sorted_strings[index] = reinterpret_cast<const unsigned char*>(entry->key);
        }
        writer_->AddString("\"<dummy>\"");
        for (int i = 1; i < sorted_strings.length(); ++i) {
            writer_->AddCharacter(',');
            SerializeString(sorted_strings[i]);
            if (writer_->aborted())
                return;
        }
    }

    void HeapSnapshotJSONSerializer::SerializeLocation(
        const SourceLocation& location)
    {
        // The buffer needs space for 4 unsigned ints, 3 commas, \n and \0
        static const int kBufferSize = MaxDecimalDigitsIn<sizeof(unsigned)>::kUnsigned * 4 + 3 + 2;
        EmbeddedVector<char, kBufferSize> buffer;
        int buffer_pos = 0;
        buffer_pos = utoa(to_node_index(location.entry_index), buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(location.scriptId, buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(location.line, buffer, buffer_pos);
        buffer[buffer_pos++] = ',';
        buffer_pos = utoa(location.col, buffer, buffer_pos);
        buffer[buffer_pos++] = '\n';
        buffer[buffer_pos++] = '\0';
        writer_->AddString(buffer.start());
    }

    void HeapSnapshotJSONSerializer::SerializeLocations()
    {
        const std::vector<SourceLocation>& locations = snapshot_->locations();
        for (size_t i = 0; i < locations.size(); i++) {
            if (i > 0)
                writer_->AddCharacter(',');
            SerializeLocation(locations[i]);
            if (writer_->aborted())
                return;
        }
    }

} // namespace internal
} // namespace v8
